To provide a locking/unlocking device for a vehicle, capable of enhancing the accuracy of detection of a fraudulent unlocking operation while securing crime-prevention properties.

A microcomputer 26 outputs a transponder driving signal from a transmission circuit 23 when receiving an ID code signal including a locking code from a door key 11 over the first receiving circuit 22. The microcomputor 26 receives a transponder signal from the door key 11 and compares a transponder code of the door key 11 with that of the microcomputer 2. In this case, when the respective transponder codes correspond to each other, the microcomputer 26 is set not to go into alarm mode. In other words, when the door key 11 is within a vehicle 2, the microcomputer 26 is not put into the alarm mode though a door lock is fastened by an operation part 12 of the door key 11.