A scanning mirror unit for scanning a beam comprises: at least one
cantilever which is formed by bonding an elastic material and a
piezoelectric material together and supported by a base at its one end;
and a movable mirror which is supported at least by a free end of the
cantilever at its peripheral part. When voltage is applied to the
piezoelectric material, the free end of the cantilever moves in a
prescribed direction to press and move the peripheral part of the movable
mirror while leaving a central part of the movable mirror at
substantially the same position to cause a tilt to the movable mirror.
With such composition of the scanning mirror unit, a reflecting member
having a sufficient thickness (e.g. some hundreds of microns) can be
employed for the movable mirror, by which a high power laser beam
effective for treatment of affected parts, etc. can be reflected finely
and durably.