An electric pump unit comprising: a unit housing; a bearing unit (15, 30) provided within the unit housing; a rotary portion comprising: a pump driving motor shaft supported by the bearing unit (15, 30) such that an axial position of a center of gravity of the rotary portion falls within an axial range of the bearing unit (15, 30), and a motor rotor comprising: a disc portion which extends radially outwards from an axial end portion of the motor shaft, and a cylindrical portion which extends from an outer circumferential portion of the disc portion towards the other axial end side and surrounds an outer circumference of the bearing unit (15, 30); and a motor stator fixed to the unit housing, characterised in that the unit housing comprises: a cylindrical motor housing; and a pump housing coupled to the other end of the motor housing, wherein a small diameter cylindrical portion is formed on the pump housing so as to extend into an inside of the motor housing, wherein the bearing unit (15, 30) is provided inside the small diameter cylindrical portion, and wherein the motor stator is provided on an inner circumference of the motor housing, wherein the motor stator protrudes further towards one axial end side than the motor rotor; wherein a substrate for a controller is fixed to the axial end portion of the motor stator at the axial end side that protrudes further; and wherein a tallest component in the controller is disposed in a portion surrounded by the motor stator on the motor rotor side surface of the substrate. a unit housing; a bearing unit (15, 30) provided within the unit housing; a rotary portion comprising: a pump driving motor shaft supported by the bearing unit (15, 30) such that an axial position of a center of gravity of the rotary portion falls within an axial range of the bearing unit (15, 30), and a motor rotor comprising: a disc portion which extends radially outwards from an axial end portion of the motor shaft, and a cylindrical portion which extends from an outer circumferential portion of the disc portion towards the other axial end side and surrounds an outer circumference of the bearing unit (15, 30); and a motor stator fixed to the unit housing, characterised in that the unit housing comprises: a cylindrical motor housing; and a pump housing coupled to the other end of the motor housing, wherein a small diameter cylindrical portion is formed on the pump housing so as to extend into an inside of the motor housing, wherein the bearing unit (15, 30) is provided inside the small diameter cylindrical portion, and wherein the motor stator is provided on an inner circumference of the motor housing, wherein a pump driving motor shaft supported by the bearing unit (15, 30) such that an axial position of a center of gravity of the rotary portion falls within an axial range of the bearing unit (15, 30), and a motor rotor comprising: a disc portion which extends radially outwards from an axial end portion of the motor shaft, and a cylindrical portion which extends from an outer circumferential portion of the disc portion towards the other axial end side and surrounds an outer circumference of the bearing unit (15, 30); and a disc portion which extends radially outwards from an axial end portion of the motor shaft, and a cylindrical portion which extends from an outer circumferential portion of the disc portion towards the other axial end side and surrounds an outer circumference of the bearing unit (15, 30); and a motor stator fixed to the unit housing, characterised in that the unit housing comprises: a cylindrical motor housing; and a pump housing coupled to the other end of the motor housing, a cylindrical motor housing; and a pump housing coupled to the other end of the motor housing, wherein a small diameter cylindrical portion is formed on the pump housing so as to extend into an inside of the motor housing, wherein the bearing unit (15, 30) is provided inside the small diameter cylindrical portion, and wherein the motor stator is provided on an inner circumference of the motor housing, wherein the motor stator protrudes further towards one axial end side than the motor rotor; wherein a substrate for a controller is fixed to the axial end portion of the motor stator at the axial end side that protrudes further; and wherein a tallest component in the controller is disposed in a portion surrounded by the motor stator on the motor rotor side surface of the substrate.