A quantum cascade laser includes: a laser structure having a first region, a second region, and a third region, the first region having an end face; a high-specific resistance region on principal surfaces of the first and second regions; a metal layer on a principal surface of the third region; a dielectric film on the end face and the high-specific resistance region; and a reflective metal film on the dielectric film, the end face and the high-specific resistance region. The first to third regions are arranged in a direction of a first axis. The laser structure has a semiconductor mesa and a semiconductor base that mounts the semiconductor mesa. The high-specific resistance region has a wall or terrace providing a difference in level at a boundary between the first and second regions, the wall or terrace extending in a direction of a second axis intersecting that of the first axis.