To make it possible to activate photothermal reaction on skin sufficiently without feeling pain so much when irradiating laser.

An adjuster 18 is mounted detachably on a spherical lens 15 around which a screw b is formed. The adjuster 18, as a spacer, keeps constant distance between the spherical lens 15 and the top part of adjuster 18 that touches to the skin. It is possible for the adjuster 18 to extend and withdraw freely by turning the screw b. The axial length of adjuster 18 is set to make the beam waist B of laser, which is concentrated with the spherical lens 15, at the position where pass through the pain spot that is distributed under the skin A, when the adjuster 18 is extended maximally.