Opening and closing device

An opening and closing device comprising:

• a casing that defines an air passage;
• a slide door that includes:
• a door main body that is configured to be slidable in a sliding direction to open or close the air passage;
• and
• a sliding gear that is disposed only on one side of the door main body in its width direction and includes first teeth in the sliding direction;
• and
• a drive gear that is configured to be rotatable around its axis line extending in the width direction and that includes second teeth in a circumferential direction around the axis line such that the first teeth and the second teeth are arranged in engagement with each other, wherein:
• when the drive gear rotates, a driving force is transmitted from the drive gear to the slide door through the sliding gear to slide the slide door;
• the door main body is configured to be restricted from shifting in the width direction due to the rotation of the drive gear;
• the drive gear is configured to support the sliding gear and to restrict the sliding gear from shifting in the width direction, thereby restricting the door main body from shifting in the width direction due to the rotation of the drive gear;
• each of the drive gear and the sliding gear is a double helical gear extending obliquely relative to the axis line;
• when approaching the center of the drive gear in the width direction, the second teeth of the drive gear on the one side in the width direction extend toward one side in the circumferential direction around the axis line;
• when distanced away from the center of the drive gear in the width direction, the second teeth of the drive gear on the other side in the width direction extend toward an opposite side from the one side in the circumferential direction around the axis line;
• when approaching the center of the sliding gear in the width direction, the first teeth of the sliding gear on the one side in the width direction extend toward one side in the sliding direction;
• and
• when distanced away from the center of the sliding gear in the width direction, the first teeth of the sliding gear on the other side in the width direction extend toward an opposite side from the one side in the sliding direction.