To provide a lock mechanism capable of preventing inconveniences from occurring even when a handle and a knob are carelessly operated during the locking.

A locking board 5 is shortened. The base end of a sub locking board 18 of the generally same length as the original locking board is installed coaxially with the locking board 5 and rotatably relative to the locking bar. The sub locking board 18 is biased in the direction approaching the dead bolt of the locking board. When the step section of the dead bolt 1 is positioned inward of the position where the step part crosses the path of the end of the locking board, a current to a motor in the locking direction is interrupted by a control switch 21 drivingly switched by the other end of the locking lever 15.