Abstract: A displacement measuring device includes: a probe having a telescopic structure capable of extending and contracting as a whole; and a measuring unit configured to measure a displacement of a front end relative to a base end of the probe, the probe includes a single cylindrical body or a plurality of cylindrical bodies having different diameters and a columnar or cylindrical front end member that is movably inserted into the single cylindrical body or the cylindrical body having the smallest diameter and of which a front end is mounted to a displacement measuring object, and the single or the plurality of cylindrical bodies and the front end member have a rotation applying mechanism that applies a rotation movement in conjunction with a forward/backward movement when the inner cylindrical body or the front end member moves forward/backward relative to the outer cylindrical body in an extension and contraction direction.