To discover the abnormality of a reinforcing plate or the like at a preceding stage up to a critical damage in a load supporting type expansion joint.

In the expansion joint 1 installed between a joint for bridge girders H1 and H2, at least composed of an upper section 3 covered with an elastic body 5, the lower reinforcing plates 2a and 2b and combining sections 7a and 7b interposed among these mutual reinforcing plates 3, 2a and 2b and constituted so as to be able to support a car travelling on the expansion joint, vibrations are generated in the expansion joint 1 by a vibration from the surface side of the expansion joint, and the response vibrations are measured and abnormality generated in the expansion joint 1 is confirmed.