The invention relates to a diagnostic device (10) of a seismic probe (1), said probe comprising, in an elongate tubular body (9), an electronic module (3), an array of capacitors (4) and a spark gap (5) suitable for generating a shock wave in a drilling well (2), said device including at least one sensor (11) suitable for measuring at least one parameter of the shock wave in accordance with time, characterised in that said sensor is attached to an inner surface of a wall of the tubular body, at a predetermined distance other than zero from the spark gap in the direction of the electronic module. The invention also relates to a diagnostic method using the signals from the sensor (11).