A simple laser interferometer is proposed. It consists of a small concave mirror, a gas laser, a semitransparent flat mirror, a concave ellipsoidal mirror under test, and a register equipment. Laser beam is reflected by very small concave or convex paraboloidal mirror and then it is directed to the semitransparent flat mirror, and to the mirror under test. The light reflected by the flat mirror is reference wave, the light reflected by the mirror under test is imperfect wave to screen or in a register equipment to obtain useful interferogramms. It is possible to test any concave ellipsoidal mirror by manufactured and tested at Crimean Astrophysuical Observatory.