Motor unit and roller with built-in motor

Provided is a motor unit for which the work of assembly when enclosing a motor and a speed reducer inside a case can be easily performed. By connecting a motor (3) provided with a rotating shaft (15), a speed reducer (4) for reducing the speed of rotation of the rotating shaft (15), and an output shaft (16) for transmitting the driving force generated by the rotation of the rotating shaft (15) to an external member so as to form a straight line and to be capable of power transmission, a serial line of shafts is formed. The motor unit (1) is formed by enclosing the formed line of shafts inside a case (2). When doing so, at least three positions in the line of shafts are supported by bearing members (5) inside the case (2). Multiple bearing installation sections (40, 41, 42) for installing the respective bearing members (5) are integrally formed on the inner circumferential surface of the case (2).