First and second optical fibers are opposed to each other, between which first and second lenses constituting a lens system having an optical axis coincident with those of the optical fibers are arranged with a gap therebetween in the direction of the optical axis. The actuators, ect are used to move the first and second lenses with electrostatic forces, in opposite directions along the optical axes of the optical fibers by the same amount at the same time. Thereby, the spot size of the light incident on the optical fiber on the reception side is changed while maintaining the light propagating between the first optical fiber and the second optical fiber point-symmetric in mode field shape. This changes the coupling efficiency between the first optical fiber and the second optical fiber, allowing an adjustment in light power.