To provide a sliding door mechanism that enables a free-stop mechanism after automatically closing a sliding door within a predetermined period of time, when opening the sliding door.

A sliding door mechanism includes: a closing-direction movement mechanism which comprises a sliding door 2, a rail 3 provided along the opening/closing direction of the sliding door 2, and a wheel 4 provided in the sliding door 2 in such a manner as to move while rotating on the rail 3, and which automatically moves the sliding door 2 to a closing position; and a free-stop mechanism 20 which stops the sliding door 2 in an arbitrary position. The sliding door mechanism comprises disabling means 80 for disabling an operation of the free-stop mechanism 20 for a predetermined period of time, when the sliding door 2 is moved in the opening direction.