A V-shaped frame 102 is attached to a pipe 100 to be drilled. The dc-to-dc converter comprises: a transformer having input and output windings; an input dc-to-ac converter coupled between dc input and input winding; and an ac-to-dc converter coupled between output winding the dc link. , a residual with a smallest value during an initialization period as an initial residual among residuals calculated by a residual calculation unit during the initialization period from timing of starting an operation of a vehicle or timing of a change in a traveling scene including a condition of traveling road of the vehicle as a starting point till a predetermined period of time elapses.