An optical filter having a transmission wavelength to be tuned dependent on light incident angle is rotatively provided in a collimated light path. The optical filter is rotated by the displacement of a piezoelectric actuator by a structure in which the displacement is converted to the rotation of the optical filter. The converting structure comprises a displacement magnifying mechanism for magnifying the displacement to provide the magnified displacement and a motion converting mechanism for converting the magnified displacement to the rotation of the optical filter.