A laser device, comprising a laser beam emitter having an optical resonator, wherein the optical resonator has a resonator and a reflection mirror, and at least one of a length of the resonator or a curvature of the reflection mirror is determined so as to satisfy condition that a parameter M.sup.2 of beam quality of a projected laser beam is within a range of 8.ltoreq.M.sup.2.ltoreq.22, where M.sup.2=.pi.W.THETA./.lamda. (W is a beam waist of a laser beam; .THETA. is a spreading angle; and .lamda. is a wavelength of the laser beam).