In an optical amplification device using a multicore optical fiber, it is difficult to efficiently amplify signal light. In order to solve this problem, an optical amplification device according to the present disclosure includes an optical fiber amplification unit including a plurality of amplification cores, a first connection unit being connected to one end of the optical fiber amplification unit, and a second connection unit being connected to another end of the optical fiber amplification unit, wherein the first connection unit is configured in such a way as to connect a transmission fiber including a plurality of transmission cores to the optical fiber amplification unit, and the number of the plurality of amplification cores is larger than the number of the plurality of transmission cores.