A laser interferometric measuring instrument includes: a light source that emits a laser beam of 1064 nm and another laser beam of 532 nm; a polarizing beam splitter; a dichroic mirror that splits a long-wavelength laser beam provided in a measurement optical path; a long-wavelength corner cube that reflects the split laser beam; a measurement corner cube that is displaceable along the measurement optical path; a reference corner cube that is displaceable along a reference optical path; a optical path changing unit that changes an optical path length of the long-wavelength laser beam; a phase detector that outputs interference signals; a sum signal computer that calculates a sum signal; a displacement controller that displaces the reference corner cube so as not to change a phase of the sum signal; a reference displacement detector that detects a displacement of the reference corner cube; and a measurement displacement computer that calculates a displacement of the measurement corner cube.