To provide a crime preventing sash lock guard mounted on an inside of a window glass near a lock receiving member of a lock part of a glass-window frame, which functions to prevent unlocking when the window glass near the lock part is broken so that a hand may be inserted from the outside therethrough for unlocking, and facilitates its mounting and removing.

The sash lock guard comprises a box-shaped base plate 2, a supporting member 3 being arranged in the base plate 2 and having engaging members 33 formed on both end sides thereof, an expansion spring 4 arranged inside the supporting member 3, a connecting wire 5 being arranged in an expansion and contraction direction of the expansion spring 4 and having a window frame engaging member 51 connected to one end thereof, and engagement receiving parts 6 with which the engaging members 33 of the supporting member 3 provided in the base plate 2 are engaged.