Abstract: A rotary boring machine comprises a base machine placed on the ground, a boring drill provided with the base machine and driven for rotation, a dip gauge provided at the tip end of the boring drill, a first circuit provided in an intermediate portion of the boring drill and electrically connected to the dip gauge for producing a varying flux corresponding to the output signal of the dip gauge, and a second circuit provided in the intermediate portion of the boring drill in opposition to the first circuit and inducting an induction current corresponding to the output signal of the dip gauge through an electromagnetic induction caused by the varying flux generated by the first circuit. The output signal of the dip gauge is transmitted by electromagnetic induction between the first and second circuits and thus transmitted to the base machine without requiring physical connection of the signal transmission lines.