A measuring device for a drilling apparatus which comprises a series of drilling rods, rotary and axially mobile. The measuring device comprises sensors, disposed on the series of rods, and feed devices of the electromagnetic induction type, able to feed the sensors electrically. Each of the devices is connected to a feed source and comprises a rotary element and a stator. A guide unit is mounted on the apparatus, and a slider, on which the stator is supported, is able to slide on the guide unit with an axial motion corresponding to that of the series of rods.