Sheet stacking device

A sheet stacking device comprising:

• a drive motor;
• a power transmission mechanism configured to transmit power from the drive motor;
• and
• a tray capable of stacking of sheets thereon, the tray configured to move up and down by the power transmitted through the power transmission mechanism, wherein
• the power transmission mechanism includes:
• a first power transmission part configured to reduce and transmit the power from the drive motor;
• and
• a second power transmission part configured to reduce and transmit the power from the first power transmission part,
• the second power transmission part includes:
• a worm gear having a gear shaft portion and a tooth portion, the gear shaft portion being rotationally driven by the power from the first power transmission part, the gear shaft portion having an outer circumferential surface, the tooth portion having a helical shape, the tooth portion being on the outer circumferential surface of the gear shaft portion;
• and
• a worm wheel engaged with the worm gear, and wherein
• the worm wheel has an engagement recessed portion,
• the engagement recessed portion is engaged with the tooth portion,
• the engagement recessed portion has a curved recessed shape corresponding to a shape of the tooth portion when viewed from a direction parallel to a worm-gear axis of the worm gear, and
• a reduction ratio of the first power transmission part is greater than a reduction ratio from the second power transmission part to the tray.