Disclosed is an optical switch for transmitting or shutting down an input light signal in accordance with a set switching state. The optical switch comprises first and second optical amplifiers connected in cascade. When an optical fiber amplifier comprising EDFs (11 and 12) and pumping sources (31 and 32) is used as the first and second optical amplifiers, the switching is accomplished by switching on or off the pumping sources (31 and 32) in accordance with control signals supplied from a control circuit (300). One input light signal can be dropped through a first optical branch (51) located on the input side of the optical switch, while another input light signal can be added through a second optical branch (53).