To obtain a good communication performance by using a communication unit detachably in an imaging device such as a digital camera or the like.

The communication unit 50 comprises: a cover closure preventing means 51b for preventing an openable cover 20 from being opened or closed; and a sensing result changing means 51a for setting the sensed result of opening/ closing sensing means 16, 21 in the state that the cover 20 is opened to a closed state. Thus, a problem that a fault occurs in a communicating function by an influence of an external appearance having a shielding effect can be solved without a complicated operation, or without increase in cost and size or an increase in a fraction defective. The operation of the imaging device can be set so as not to be limited even in the state that the cover is opened only at a communication unit mounting time, and the communication can be realized without failure. When a memory card or the like except the communication unit is mounted as a mounting unit, the operation of the imaging device can be limited so as not to introduce an electrical damage or the like of the unit due to the attaching/detaching of the mounting unit.