Worm

A worm with which a gear is meshed, the worm comprising:

• a main body part;
• a first tapered part connected to one axial side of the main body part and having a tapered shape that tapers off from the main body part;
• a second tapered part connected to another axial side of the main body part and having a tapered shape that tapers off from the main body part;
• a spiral tooth provided in a spiral shape on outer circumferential parts of the first tapered part, the main body part, and the second tapered part, and comprising a tooth tip part and a tooth bottom part;
• a first tooth bottom end part provided at the first tapered part and forming one end part of the tooth bottom part;
• and
• a second tooth bottom end part provided at the second tapered part and forming another end part of the tooth bottom part, wherein
• the tooth bottom part extends to advance in a spiral shape from the first tooth bottom end part toward one circumferential side of the worm, and a position of the second tooth bottom end part is configured within an angle range of less than 90 degrees on another circumferential side of the worm with respect to a position of the first tooth bottom end part, centered on a rotation center of the worm.