A gas-leak detector includes a suction pump that sucks sample gas and reference gas, two gas detection sensors, and a cell block having a cell therein. The cell receives the gasses and has two suction-gas introduction channels and a single gas discharge channel opening thereinto. The gas-leak detector detects a gas leak on the basis of outputs from the sensors. The introduction channels and the discharge channel open into the cell at a first one of opposing surfaces of the cell, the opening of the discharge channel being arranged between the openings of the two introduction channels. The sensors are on the same plane as a second one of the opposing surfaces and are arranged between the opening of the discharge channel and the openings of the introduction channels. The suction pump is arranged on the cell block and communicates with the opening of the discharge channel.