To provide a laser-interferometer type displacement gauge, provided with a ring laser resonator as a dual-frequency ring laser light source.

The laser-interferometer type displacement gauge is provided with a displacement detecting mirror 42, mounted to a body under displacement detection of receiving and reflecting one laser light among dual-frequency laser beams emitted to outside via a laser beam extracting part from the double- frequency ring laser light source and feeding the one laser light back to the laser beam extracting part, a receiver 52 for output for superposing the reflected light at the laser beam extracting part of the feedback light which is fed back from the displacement detecting mirror 42 on the other laser beam among the dual-frequency laser light emitted to outside from the laser beam extracting part to from optical beat, receiving the optical beat as a detection signal, and photoelectrically converting it, and a signal processing part 5 for processing the received electrical signal of the receiver 52 for output to create a signal, which indicates displacement of the body to be distortion detected.