Sheet feeding device and image forming system

A sheet feeding device comprising:

• a feeding roller pair configured to feed a sheet;
• a first guide configured to form a feeding passage along which the sheet fed by said feeding roller pair is passed;
• a door provided with a second guide forming the feeding passage in cooperation with said first guide and configured to be rotatable about a shaft between a closed position and an open position, the closed position being a position where said second guide opposes said first guide and forms the feeding passage, and the open position being a position where said door is rotated in a first direction so that a center of gravity of said door passes through above said shaft with respect to a vertical direction and where the feeding passage is open;
• a damping mechanism configured to impart a first resisting force to said door when said door is rotated in a second direction opposite to the first direction;
• and
• an engaging portion including an elastic member for imparting a second resisting force to said door by being elastically deformed when said door is rotated toward the closed position, said engaging portion being engageable with a portion-to-be-engaged at the closed position,
• wherein when said door is rotated from the open position to the closed position, said door passes through (1) a first position where the center of gravity is positioned above said shaft with respect to the vertical direction, (2) a second position where the center of gravity is positioned on a downstream side, with respect to the second direction, of the first position, and (3) a third position where (a) the center of gravity is positioned on a further downstream side, with respect to the second direction, of the second position and (b) said elastic portion starts elastic deformation,
• wherein the first resisting force is set so that a moment acting around said shaft by a self-weight of said door is larger than the first resisting force of said damping mechanism when said door is positioned between the second position and the third position, and
• wherein a resultant force of the first resisting force of said damping mechanism and the second resisting force of said elastic portion is set so that the moment acting around said shaft by the self-weight of said door is larger than the resultant force when said door is positioned between the third position and the closed position.