To provide a drain pump unit for protecting an electric motor and counter-measures against pump noise.

An electric motor is mounted on the upper parts of housings 1 and 2, each partitioned into upper and lower chambers by a partition wall 4 to prevent influence from being exercised on an electric motor 19 for driving a pump by drain the surface of which is raised as a result of agitation and reverse flow drain from a drain piping. A air inlet port 9 and a drain discharge port 10, with one positioned above and the other positioned below, are opened to the lower chamber of the housing to form a pump chamber, and a pump suction port 11 positioned in a drain pan is opened to a lower end. Impellers 13 are rotationally situated in a pump chamber and positioned respectively in upper and lower chambers to prevent the generation of an abnormal load applied on the electric motor, and the electric motor and the impeller are shaft-coupled together through a magnetic shaft coupling, consisting of a magnet 20 on the electric motor side and a magnet 23 on the impeller side, which are positioned in the upper and lower chambers with the magnets positioned opposite to each other and with a partition wall located therebetween, to prevent an abnormal load from being exerted on the electric motor. As a measure for countering pump noise, the tip of an air inlet piping coupled to the air inlet port is positioned in a spot where no problem arises, and a muffler is attached directly to its tip or the air inlet port.