A heterodyne laser having a first optical path for guiding excitation light and a second optical path for guiding measurement light. The heterodyne laser includes an optical probe body for optically coupling and structurally combining the first optical path and the second optical path, and includes a reflection mirror, a beam splitter, a focal lens and a 1/4 wavelength plate. The excitation light from the first optical path is introduced through the reflection mirror, the beam splitter and the focal lens into a measurement object.