A displacement measuring device comprising: a probe configured to have a telescopic structure that is 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 including a single cylindrical body or a plurality of cylindrical bodies having diameters different from each other 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 of the plurality of cylindrical bodies 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 having 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, wherein the measuring unit includes: a displacement detecting unit (50, 60) detecting the displacement of the front end relative to the base end of the probe in the extension and contraction direction, characterized in that the measuring unit further includes: a mounting mechanism (41, 41b-41f) that rotatably mounts the base end of the probe around a first axis (x) extending in a first direction crossing the extension and contraction direction, and a second axis (y) extending in a second direction crossing the extension and contraction direction and the first direction, a first rotation displacement meter being mounted on the mounting mechanism to detect a rotation angle around the first axis, and a second rotation displacement meter being mounted on the mounting mechanism to detect a rotation around the second axis. a probe configured to have a telescopic structure that is 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 including a single cylindrical body or a plurality of cylindrical bodies having diameters different from each other 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 of the plurality of cylindrical bodies 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 having 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, wherein the measuring unit includes: a displacement detecting unit (50, 60) detecting the displacement of the front end relative to the base end of the probe in the extension and contraction direction, characterized in that the measuring unit further includes: a mounting mechanism (41, 41b-41f) that rotatably mounts the base end of the probe around a first axis (x) extending in a first direction crossing the extension and contraction direction, and a second axis (y) extending in a second direction crossing the extension and contraction direction and the first direction, a first rotation displacement meter being mounted on the mounting mechanism to detect a rotation angle around the first axis, and a second rotation displacement meter being mounted on the mounting mechanism to detect a rotation around the second axis. a displacement detecting unit (50, 60) detecting the displacement of the front end relative to the base end of the probe in the extension and contraction direction, characterized in that the measuring unit further includes: a mounting mechanism (41, 41b-41f) that rotatably mounts the base end of the probe around a first axis (x) extending in a first direction crossing the extension and contraction direction, and a second axis (y) extending in a second direction crossing the extension and contraction direction and the first direction, a first rotation displacement meter being mounted on the mounting mechanism to detect a rotation angle around the first axis, and a second rotation displacement meter being mounted on the mounting mechanism to detect a rotation around the second axis. a mounting mechanism (41, 41b-41f) that rotatably mounts the base end of the probe around a first axis (x) extending in a first direction crossing the extension and contraction direction, and a second axis (y) extending in a second direction crossing the extension and contraction direction and the first direction, a first rotation displacement meter being mounted on the mounting mechanism to detect a rotation angle around the first axis, and a second rotation displacement meter being mounted on the mounting mechanism to detect a rotation around the second axis.