A pump apparatus includes a motor unit and a pump unit. The motor unit includes a cylindrical yoke housing and a rotor accommodated in the yoke housing. A rotary shaft of the rotor is supported by a first bearing and a second bearing. In a direction from a bottom wall of the yoke housing toward an opening of the yoke housing, the first bearing, an armature, a commutator, and a second bearing are arranged in this order on the rotary shaft. A base plate is attached to the opening of the yoke housing. The base plate has a through hole for receiving the second bearing. The commutator has an outer diameter greater than the inner diameter of the through hole. A disc spring is located between the bottom wall and the first bearing. The disc spring urges the rotor in a direction from the bottom wall toward the opening.