In an attachment stage 20 of an adapter device 10, a fastening unit 221 fastened to a main body device is provided on an attachment surface 21 in advance. A connector 55 is provided on a housing 50. Further, the adapter device 10 is provided with a movement direction conversion unit configured to convert a movement in an operation direction of an operation lever 41 into an insertion and detachment direction of the connector, and move forward and backward the housing 50 in the insertion and detachment direction of the connector 55 with respect to the attachment stage 20 in accordance with the operation force. In the movement direction conversion unit, a first link mechanism converts the movement in the operation direction of the operation lever 41 into a movement in a surface direction of the attachment surface 21 of a hook unit 321f, and a second link mechanism converts the movement in the surface direction of the hook unit 321f into the movement in the insertion and detachment direction of the connector of the housing 50 with respect to the attachment stage 20. The hook unit 221f of the 221 is fastened to the main body device and the operation lever 41 is operated, so that the insertion and detachment operation of the connector can be performed in a stable manner.