A lock for an antitheft device for a motor vehicle steering column is provided and includes a stator having a stator head with an opening, a rotor rotatably mounted about an axis with respect to the stator having an annular flange, a cam to rotate as one with the rotor, and an elastic element arranged between the cam and the rotor in order to exert a thrust load axially on the rotor. The opening of the stator is designed to engage with the annular flange to prevent the rotor from rotating in a predetermined rotation direction from a predetermined angular position and allows the rotor to rotate beyond the predetermined angular position by prior depression of the rotor.