A diaphragm pump includes a pump chamber, a diaphragm, and a diaphragm deformer. The pump chamber is box-shaped and includes at least an inlet opening, an outlet opening, and a diaphragm attaching opening. The pump chamber is provided with an inner space. A diaphragm is made of an elastically deformable material, and is provided in the pump chamber so as to cover the diaphragm attaching opening. The diaphragm deformer elastically deforms the diaphragm to change a capacity of the inner space. The outlet opening is located at a highest position in the inner space of the pump chamber.