A slide unit mechanism includes a sliding plate including slide parts and rattle preventing mechanisms that engage the sliding plate to prevent the sliding plate from rattling. Each of the rattle preventing mechanisms includes a recess; an opening positioned on a moving path of the slide part; a locking torsion spring disposed in the recess, one end of which is attached to an engaging part protruding from the opening on the moving path of the slide part; and an engaging recess formed in the slide part and configured to engage the engaging part. When the sliding plate is slid to the open position or the closed position, the engaging part engages the engaging recess and is biased by elastic force of the locking torsion spring toward the engaging recess.