Thread motor and playback device

A playback device, comprising:

• a chassis;
• a thread motor provided at the chassis;
• a transmission gear group transmitting power of the thread motor to a playback portion;
• and
• a motor falling prevention portion provided at the chassis and preventing the thread motor from falling away from the chassis;
• wherein the thread motor includes a first gear and a flange portion at an outer peripheral surface of a cylindrical rotor, and the first gear and the flange portion are arranged so as to be opposed to each other with a predetermined clearance;
• and
• wherein the motor falling prevention portion prevents a falling of the thread motor by a tip portion thereof touching the flange portion when the thread motor moves in a falling direction away from the chassis;
• wherein the transmission gear group includes:
• a second gear engaging with the first gear provided at the outer peripheral surface of the thread motor,
• a third gear which is coaxial with the second gear and arranged between the chassis and the second gear,
• a fourth gear engaging with the third gear,
• a fifth gear engaging with the fourth gear, and
• the second gear is a flat-plate gear, the third gear is a first worm gear, the fourth gear is a shaft-shaped worm gear and the fifth gear is a second worm gear
• wherein, in the fourth gear, one end side and another end side have reverse threads, taking an approximate center of the fourth gear in a longitudinal direction as a boundary, one end side engages with the third gear and the other end side engages with the fifth gear.