A depriming device and a relative method for the removal of the primer from the head of cases of cartridges for firearms are described. The device includes a depriming mechanism, a device for positioning and restraining at least one case on a surface plate, at the depriming mechanism, and a movement device to shift the depriming mechanism from a raised position, in which the latter is moved away from the case to be deprimed, to a lowered position, in which it comes into contact with the primer of the case and push it thereby causing its detachment from the case itself.