To provide a roller with built-in motor, facilitating the assembling of a roller conveyor.

The roller 3 with built-in motor includes a roller body 11 of a cylindrical shape, in which a motor 12 and a reducer 13 are built-in. The roller 3 with built-in motor has fixed shafts 20 and 21 protruding out of both ends of the roller body 11. One fixed shaft 20 has a hollow shape, in which a fixed-side connector piece 25 is built-in. A free-side connector piece 33 is connected with the fixed-side connector piece 25 in the roller 3 with built-in motor.