The recording medium 12 is radiated with light beam from the second light source to obtain servo signal from the reflected light. At least one of the relay lenses 8 in the relay optical system is moved perpendicularly to the optical axis according to the servo signal to follow-up moving direction of the recording medium. The light beam from the second laser light source merges with an optical system from the first laser light source to the recording medium 12 between at least one of the relay lenses 8 and the spatial light modulator 3.