In a light source device, an axis extends from a light-emitting face and perpendicularly to the light-emitting face. A reflective surface includes a curved surface defined by rotating a first arc which is a part of an ellipse around the axis. The ellipse has a first focal point and a second focal point which are located on the light-emitting face. The second focal point is located adjacently to the first arc with respect to a center of the ellipse. A distance from the first focal point to the axis is shorter than a distance from the second focal point to the axis.