A lateral slide member includes first locked portions and a second locked portion and is configured to be displaced between a first lock position and a first release position. A vertical slide member includes a second locking portion that restricts the lateral slide member from being displaced from the first lock position to the first release position, the vertical slide member configured to be displaced between a second lock position and a second release position. A swing member includes a contacted portion and a third locking portion. A cover projection portion includes a third locked portion that is locked to the third locking portion and thereby restricts a document sheet cover from moving upward. When a document sheet reading unit is closed, a main body projection portion pushes up the contacted portion to hold the swing member at a third release position, allowing the contacted portion to extend diagonally upward.