Provided is a device for determining a wheel fastening state that allows a wheel fastening state to be monitored during running. The device includes a sensor unit (3) that is attachable to and detachable from a wheel fastening part, an information terminal (4) that is an in-vehicle device (4A) or a portable terminal (4B), and a server (30). The terminal (4) includes a measurement instruction module (23) to read vehicle state data from a control and communication system (5) of a vehicle and send an instruction for to measurement to the sensor unit (3) at determined timing. The server (30) includes a first information processing module (32) configured to determine an abnormality of a fastening state of the wheel fastening part by comparing the measurement data with accumulated data that is measured under the same condition and stored in the past.