A door mechanism for disposing on a bin body, which has an inner periphery defining an opening, includes a door panel unit configured to be pivoted to the inner periphery of the bin body to openably close the opening, a hinge unit configured to pivotally connect the door panel unit to the inner periphery of the bin body, a rotary wheel unit for controlling rotation of the hinge unit, a drive unit pivoted between the rotary wheel unit and the hinge unit, and a motor unit for driving rotation of the rotary wheel unit. When the rotary wheel unit is driven by the motor unit to rotate, the rotary wheel unit drives rotation of the drive unit which in turn drives the hinge unit to rotate said door panel unit to an open or a closed position.