Abstract: A laser interferometer includes a laser light source, a collimator generating collimated light, an optical modulator modulating the collimated light into reference light having a different frequency, and a light receiving element receiving object light and the reference light and outputting a light receiving signal. An optical axis of the collimated light is a first optical axis. When return light is generated, an optical axis of the return light is a second optical axis. A position at which the collimated light is generated is a reference position. The first and second optical axes at the reference position has a shift width ?y. The collimator has an effective diameter ?. The collimated light has a light diameter R. The reference position is away from the optical modulator by a distance L. The collimated light has a wavelength ?. These properties satisfy a specific equation (A).