To provide a tire/wheel theft detecting device that can be attached easily to an existing vehicle while suppressing the occurrence of malfunction.

A detecting unit 100 detecting acceleration in the X-axis direction generated in a tire rotating direction, acceleration in the Y-axis direction generated in a tire rotation axis direction, and acceleration in the Z-axis direction generated in a direction orthogonal to a tire rotation axis, and sending information on the acceleration by a radio wave is provided in each tire. The acceleration information from the detecting unit 100 is received by a monitoring unit 200 provided in the vicinity of a driver's seat, and moreover, the change pattern of the received acceleration in a predetermined time and a change pattern stored in advance in the monitoring unit 200 are compared, and a theft alarm is raised when the change pattern is out of a permissible range.