Power transmission device

A power transmission device which transmits power to an operation portion, comprising:

• a motor having a motor case disposed in a housing,
• a worm connected to a rotating shaft of the motor, and
• a worm wheel engaged with the worm and disposed at an operation portion side with respect to the worm,
• wherein a biasing member is disposed at the one side with respect to engagement portions of the worm and the worm wheel;
• said biasing member being operable to bias one side of a worm wheel side and a worm side in a direction in which the worm and the worm wheel come in contact with each other when the motor is driven;
• wherein said housing comprises a first restriction wall located on one end side in a rotating shaft direction with respect the motor case, and a second restriction wall located on the other side in the rotating shaft direction with respect to the motor case;
• wherein the biasing member is located between the first restriction wall and the motor case at a position spaced away from the worm such that one end of the biasing member is in direct contact with the first restriction wall and the other end of the biasing member is in direct contact with the motor case;
• wherein the biasing member is separate from the motor;
• and
• wherein the biasing member is arranged around the rotating shaft such that a gap is formed between periphery of the rotating shaft and the biasing member.