This surface light source device has; a case; multiple light-emitting devices arranged on the inner surfaces of a pair of side walls within the case; a reflecting member that protrudes from the base surface of the case, and that reflects light emitted from the light-emitting devices toward an aperture part of the case; and a light-emitting surface member that has a light-diffusing property and a light-transmitting property, and that covers the aperture part. The light-emitting devices are arranged on the side walls such that the light axis of the light-emitting elements is parallel to the base surface of the case. The light-reflecting member has a ridge line that is parallel to the side surfaces and the ceiling surface of the case, and the light-reflecting member is formed with a curved surface, with the ridge line being contained in the apex thereof.