Sheet processing apparatus

A printer, comprising:

• a main body including an insertion slot;
• an image forming unit in the main body and configured to form images on sheets of paper;
• a sheet cassette for supplying sheets of paper to the image forming unit and configured to be inserted into the main body via the insertion slot and removed from the main body via the insertion slot, the sheet cassette including a pin member extending in a first direction orthogonal to an insertion direction of the sheet cassette, the pin member being connected to the sheet cassette so as to be moveable in a second direction orthogonal to the first direction and the insertion direction;
• and
• a housing in the main body and including:
• a lever partially rotatable about a first axis proximate to a first end of the lever, the first axis being parallel to the first direction, the lever having a pin engagement portion at a tip portion at a second end of the lever opposite the first end, the pin engagement portion being rotatable about a second axis parallel to the first direction and having an engagement groove into which the pin member can be inserted from a first pin engagement position and a second pin engagement position when the lever has rotated about the first axis, the engagement groove having a first sidewall and a second sidewall, a contact surface portion of the engagement groove being continuous with the first sidewall;
• an elastic member configured to apply a force to the lever to rotate the lever toward the insertion direction, the elastic member being connected to the lever at a position between the first axis and the pin engagement portion;
• and
• a chassis having a guide groove formed therein, the guide groove extending along the insertion direction and controlling the position of the pin member in the second direction, wherein
• the contact surface portion is curved in a convex shape in a direction away from the first sidewall, and
• the contact surface portion contacts the pin member when inserted from the second pin engagement position when the lever has rotated maximally in the insertion direction.