To prevent articles inserted into a case from being stolen by drawing them when the articles are aligned and displayed on the shelf of a shop.

The antitheft device is so constructed that in the case K of a type where the article A is freely inserted and housed from openings 1 provided on one surface of the periphery, a fitting body B is detachably fitted into the external surface of the case so as to partially close the opening, a protrusion 8 for preventing the disengagement of the fitting body is provided by fitting the end of the opening inside one end of the fitting body and hitching at the case, in addition, a suitable engagement means C which is pressed back to the other end of the fitting body and the case when the fitting body is fitted thereinto, and is engaged with them when the fitting is completed is provided.