Re “Humidifier”


This case stems from a patent invalidation trial conducted by the Japan Patent Office (JPO) in which the patent was found invalid. The case was then appealed to the Intellectual Property High Court which overturned the former decision rendered by the JPO.

Legal Issue:

The issue concerns whether the claimed feature of  “when the control module receives a detection signal from a tray water-level detection module in an auxiliary tray during humidifying operation, for which a fan rotates, then the rotation of the fan is continued until the lapse of a predetermined period of time” (paraphrased into English) could easily have been made.

Summary of Conclusions:

The Court interpreted a main reference of the prior art, as disclosing that “water level detected at a first reference position H1″ (paraphrased into English) refers to a lower threshold (water level) corresponding to a liquid level necessary for a humidifying module to appropriately generate humidified air, and that when a liquid level (i.e. water level) lower than the threshold is detected, then the operation of the humidifying module is stopped. The Court decision further refers to a secondary reference of the prior art, as disclosing a humidifier having a motor that is rotated over a predetermined period or more after a water level is detected as being lower than “a certain water level,” (paraphrased into English) and further disclosing a low-speed rotation of the motor, enabling a longer period of humidification. The Court reasoned that “a certain water level” described in the secondary reference is clearly different from “contact point at the first reference position” in the main reference, in terms of whether a humidifying function can appropriately operate even at a water level lower than the contact point. The Court further opined that there is no motivation to replace “contact point at a first reference position” in the main reference with the configuration for detecting “a certain water level” of the secondary reference.  Further, according to the Court, if “contact point at a first reference position H1″ of the main reference is replaced with the use of “a certain water level” from the secondary reference as a detection target, then the effect of the main reference of preventing wasteful operation of the fan is inhibited, and that there is thus a disincentive to combine the two references.

(Note) An English summary by the Intellectual Property High Court is available here.



The defendant asserted that the technical problem to be solved by the invention in question is a cost increase caused by solving with “two contact points” (translated to English) as in the main reference, and that the second reference discloses solving the same technical problem as the invention in question; and that consequently, there is a strong motivation to combine the references.  However, the Court disagreed that the cited invention has as an object to solve the cost increase caused by having two contact points, and thus, rejected the defendant’s assertion.