Sheet stacking device and image forming apparatus provided with same

An image forming apparatus, comprising:

• an image forming portion for forming images on sheets;
• and
• a sheet stacking device to which the sheets are to be discharged;
• the sheet stacking device including:
• a device main body;
• a sheet discharge unit arranged in the device main body and configured to discharge sheets;
• a sheet stacking portion arranged in the device main body and including a sheet stacking surface on which the sheets discharged from the sheet discharge unit are to be stacked;
• an opening formed in the sheet stacking surface;
• and
• a sheet detector including:
• a first sheet detector with a rotatable actuator that includes a detection piece capable of projecting upwardly out of the opening in the sheet stacking surface and retracting into the opening in the sheet stacking surface according to rotation of the actuator, the detection piece being capable of detecting a first state where no sheet is placed on the sheet stacking surface and a second state where a first number of the sheets discharged from the sheet discharge unit are placed on the sheet stacking surface;
• and
• a second sheet detector having a housing that is rotatably supported by the device main body, the housing of the second sheet detector rotatably supporting the actuator, the second sheet detector being capable of detecting a third state where a second number of the sheets are placed on the sheet stacking surface, with the second number being larger than the first number, the second sheet detector being capable of detecting the third state according to rotation of the housing with the actuator pressed by the second number of the sheets.