To provide a burglar prevention implement capable of being manufactured at a low cost, being easily handled, having reliability and being widely used.

Supporting members 4 and 4 having axial holes at the upper surface of a base body 3 are separately erected, a pin engaging hole 6 is formed at the other end, two projections are formed in an intermediate section by separating them in the direction of the width, two fitting holes are formed by separating both projections, and a burglar prevention implement is composed of a base stand 2 having a locking key hole 12 and an unlocking key hole 13 at both projections and a connecting member having an axial hole at the lower surface near to the end of an arm body 21 are formed, a pin 29 is vertically provided on the lower surface of the other end, a lock arm 20 having a fitting member 26 having a fitting projection providing a locking key groove to the lower surface of the intermediate section of the arm body 21, a connecting shaft 30 supporting the base stand and a lock arm in a rotatable manner and an elastic spring key. The lock arm is locked to the base stand by inserting the spring key from the locking key hole of the side of the projection by fitting the fitting projection of the lock arm to the fitting hole of the base stand, and it cannot be rotated.