To provide a booster type motor cylinder which can produce great thrust around the pushing-out end of an output rod and can use a motor of relative small type and low output.

This booster type motor cylinder is an output rod 6 which drives the rotation of a drive shaft 8 with a motor 7 and pushes out and pulls back axially an output rod 6 screwing with the drive shaft 8 through a threaded part. A piston 9 fixed at the end of the output rod 6 is inserted in a cylinder chamber 20, and an accumulator 15 which supplies pressure fluid into the cylinder chamber 20 is provided. A booster ram 11 is formed, which enters the cylinder chamber 20 around the push-out final end of the output rod 6 and raises fluid pressure in the chamber.