A sensitivity adjustment device adjusts radio wave sensitivity of an antenna which wirelessly transmits/receives a signal to/from an external device. The sensitivity adjustment device includes a case and a ring-shaped rotating member. The case houses the antenna. The rotating member is disposed on the outside of the case in such a way as to be rotatable. The rotating member includes (a) a shielding part which shields a radio wave and (b) a penetration part which allows penetration of a radio wave. A positional relationship between (a) the antenna and (b) the shielding part and the penetration part is changed by rotation of the rotating member so that the radio wave sensitivity of the antenna is adjusted.