An automatic sharpening of chain saw has

This device comprises a main body 1 for mounting on a chain saw body, a stone support block sharpening 3 which is urged forwardly relative to the body 1 by a spring 14, a screw 2 which is screwed into the body 1 and which is rotatable so as to move the block 3 forward or backward relative to the main body 1, a sleeve-shaped part 10 which is carried by the body 1 in such a manner that it can be moved forward or backward and they can rotate in order to vary its angular position, and of which a rear end portion protrudes rearwardly and outwardly with respect to a rear end portion 12 of the body 1, a stone rod hone 18 which is carried in rotation by the sleeve-shaped part 10, which a front end portion, engaged in the block 3, a stone holder 17 and of which a rear end portion protrudes outwardly r contribution to the rear end portion of the sleeve-shaped part 10, of the immobilizing means 15-16 for maintaining the stone 17 in the rear position, against the force of the spring 14, and a handle 13 provided on the rear end portion of the sleeve-shaped part 10 in order to be able to operate the immobilisation means 15-16.