To allow an electronic control unit to detect the presence of a locking state of a vehicle buckle in a detection device for detecting the locking state.

In this device detecting a locking state of a buckle by providing a microswitch 40 or an electronic switch 30 to a buckle 1, both the microswitch 40 and the electronic switch 30 are provided inside the buckle 1, a control resistance is connected to the microswitch 40, a voltage value applied to the control resistance is controlled according to operation of the microswitch 40, a switching element and a control resistance controlling operation of the switching element are connected to the electronic switch 30 provided to an electronic control unit ECU, and the electronic control unit ECU detects a control resistance value according to the operation of the switching element.