An optical head includes a fixed part, a movable part movably held by a
plurality of wires fixed on the fixed part, and magnets fixed to the
fixed part. The movable part includes a movable-part housing, a heatsink
held by the movable-part housing, a light emitting element and a light
receiving element both mounted on the heatsink, magnets provided to both
sides of the movable-part housing to contact the heatsink, an objective
lens held by the movable-part housing to allow an emitted laser beam from
the light emitting element to focus, and a diffraction grating provided
between the objective lens and the light emitting element and between the
objective lens and the light receiving element. The gap between each coil
and the adjacent magnet is filled with ferrofluid having a higher thermal
conductivity than the atmosphere.