Rotation drive device, image reading device, and image forming apparatus

A rotation drive device comprising:

• a driven rotation member;
• a driving rotation member to receive rotational driving force from a driving source;
• a rotation relay member to transmit only a unidirectional rotational driving force from the rotational driving force of the driving rotation member to the driven rotation member;
• a shaft;
• and
• a holder to hold the driving rotation member,
• wherein the driven rotation member, the rotation relay member, and the driving rotation member have through holes, through which the shaft passes, including center axis lines of the driven rotation member, the rotation relay member, and the driving rotation member,
• wherein the rotation relay member includes:
• a housing rotatable with the driven rotation member;
• and
• a cylindrical one-way clutch disposed at an inner peripheral side of the housing,
• wherein a contact portion between the driving rotation member and the shaft is configured to rotate the driving rotation member and the shaft in conjunction with each other to transmit the rotational driving force of the driving rotation member to an inner peripheral side of the cylindrical one-way clutch via the shaft,
• wherein the driving rotation member includes a boss that is projected toward the holder and is rotatably held in a supporting hole of the holder, and
• wherein a portion of the shaft to support the driving rotation member and an inner wall surface of the through hole of the driving rotation member are shaped to rotate the shaft and the driving rotation member together.