To provide a detaching/attaching device capable of suitably detaching/attaching a card attached to a stuff to be carried, a display changing device equipped with the detaching/attaching device, and an administration system equipped with the detaching/attaching device.

A display changing device 1 comprises a detaching/attaching device 2 and a card display changing device 3, which are connected together to be integrated. A card detaching/attaching device 1 has a pressure receiving wall 23e on its back surface side, and a position adjusting mechanism 100 on a back surface side of the pressure receiving wall 23. The position adjusting mechanism 100 comprises a seat part 101, a moving part 102, and an activating part 103, the position adjusting mechanism 100 is designed to push and move the card detaching/attaching device 1 by an eccentric cam 112. The eccentric cam 112 can get away from the pressure receiving wall 23e, on condition that a reaction force Fr received by the eccentric cam 112 becomes greater than a force Fa to draw the moving part 102 to the pressure receiving wall 23e side, in the position adjusting mechanism.