Clutch unit

A clutch unit comprising:

• a first housing which is provided with a groove recessed inwards;
• a second housing which is inserted to the groove of the first housing, and is provided with first arc portions to protrude along a circumference thereof on one surface thereof;
• first roller portions which are positioned between the first arc portions;
• a first rotation transfer portion which is inserted to the second housing and is rotated in accordance with rotation of a motor;
• and
• a speed change portion which is coupled to an other surface of the second housing and changes relative rotation speeds of the first housing and the second housing to attach and detach the first roller portions to and from the first housing,
• wherein rotation of the first housing is controlled by the first rotation transfer portion and the first housing is not rotatable by external force when the first housing is attached to the first roller portions, and is freely rotatable by external force when the first housing is detached from the first roller portions, and
• wherein the speed change portion reduces a speed of the second housing by friction.