An optical element includes a gain chip, a ring modulator, which is a band-pass filter, a first optical waveguide and a second optical waveguide that are optically connected to the ring modulator, and a heater, wherein the first optical waveguide and the second optical waveguide are formed to be equal in optical path length (have no difference in optical path length) between a first light coupling point and a second light coupling point and equal in shape and length between the first light coupling point and the second light coupling point (to be symmetrical with the ring modulator interposed therebetween (with respect to the ring modulator)).