Disclosed herein is a cooler of a semiconductor laser. The cooler includes a heat sink comprising a first surface and a second surface opposite the first surface; a first conductive layer and a second conductive layer, disposed on the first surface and not short-circuited to each other; and a conductive connector comprising a first end part, a second end part, and a first connection part connecting the first end part and the second end part. The first end part is on the first conductive layer. The second end part is on the second surface of the heat sink and insulated from the heat sink. The first connection part is disposed at a first non-opposite end of the first conductive layer on the heat sink.