A parameter processing device that allows setting of a critical parameter value includes a movable slide operator on a scale of a predetermined length, and two fine-adjustment switches provided integral to the slide operator. In the operation of setting a parameter value, a rough parameter value is set by moving the slide operator. Then, one of the fine-adjustment switches is depressed to fine-adjust the set rough parameter value. Here, the level of the depressed pressure is detected by an internal pressure sensor. The detected level of the depressed pressure is converted into a corresponding fine-adjustment granularity. The rough parameter value is updated using the obtained fine-adjustment granularity. Thus, a fine parameter value can be set easily that could not previously be set by just moving the slide operator. The setting of a parameter having a wide range can easily be carried out even in a limited region.