FIG. 7 shows an example internal configuration of the operation device shown in FIG. 6. Note that FIG. 7 shows only a part of the configuration inside the housing 21. As shown in FIG. 7, the operation device 20 includes the movable portions 23A to 23D provided inside the housing 21. Note that where the movable portions 23A to 23D are not distinguished from each other, the designation “movable portion 23” may be used to refer to any of the movable portions 23A to 23D.As shown in FIG. 7, the movable portions 23A to 23D are connected to the operation buttons 22A to 22D, respectively. That is, the movable portion 23A is connected to the operation button 22A, the movable portion 23B to the operation button 22B, the movable portion 23C to the operation button 22C, and the movable portion 23D to the operation button 22D. The movable portion 23 moves (downward in the present embodiment) in response to an operation on the operation button 22 connected thereto. In the present embodiment, each operation button and a movable portion connected thereto are configured as an integral part. Note however that the movable portion may be configured so as to be moved in accordance with the movement of the operation button, and an operation button and a movable portion connected thereto may be separate parts in other embodiments.In the present embodiment, at least a portion of the movable portion 23 (the hatched area shown in FIG. 7: hereinafter referred to as a “recognition portion”is of a material (color) such that the infrared camera 4 can distinguish this portion from other portions (other than the portion of the reference marker 21d) of the wall surface on the inside of the housing 21. The recognition portion may be of a retroreflective material, for example. Then, the infrared light from the illuminating section 7 is reflected more toward the infrared camera 4, making it easier for the infrared camera 4 to recognize the recognition portion. This also makes it easier for the infrared camera 4 to recognize a recognition portion that is located away from the infrared camera 4. The movable portion 23 is connected to the lower portion of the operation button 22. Here, for each of the movable portions 23A to 23C, the recognition portion is placed under (directly below) the corresponding operation button 22. For the movable portion 23D, on the other hand, the recognition portion is displaced from a position that is directly below the corresponding operation button 22D (see FIG. 7). That is, the recognition portions of the movable portions 23A to 23D are arranged so that the recognition portions are visible through the hole 21a.