A first arm portion and a second arm portion are provided so as to have a distance therebetween greater than a distance between input ends of two output waveguides and greater than a distance between an output end of a first output portion and an output end of a second output portion, the first arm portion forming a traveling path of light from one of the two output waveguides to the first output portion through a first optical amplifier, the second arm portion forming a traveling path of light from another one of the two output waveguides to the second output portion through a second optical amplifier. The first optical amplifier and the second optical amplifier have curved portions in which the first output portion and the second output portion are curved in a direction toward each other, and the first optical amplifier and the second optical amplifier respectively output light from the output end of the first output portion and the output end of the second output portion.