A self-sustained pulsating laser diode in which a region in an active layer functions as a saturable absorber has at least five and no more than ten quantum wells, p-type cladding layer flat part with a layer thickness of at least 300 nm and no greater than 500 nm, and a p-type cladding layer flat part with a carrier density of at least 11017 cm3 and no greater than 51017 cm3. The spring strut has an outer tube having one end sealed by a piston rod guide, a working cylinder received inside the outer tube, and a hollow piston rod extending into the working cylinder through the piston rod guide. The plurality of spherical lenses are adjustable such that a selected spherical lens may be aligned with the viewing aperture. Terminal contact portions are present where the terminals contact a respective apparatus side contact forming member.