A device is provided with a PWM signal generating circuit, a gate driver and a transmission line connecting them. The transmission line transmits a PWM signal output from the PWM generator as an input signal for the gate driver. A noise suppression member is provided to at least a part of a periphery of the transmission line. The noise suppression member has a structure that magnetic powder is dispersed in a binder and has an imaginary part μ″ of a complex magnetic permeability that is greater than or equal to 5 and smaller than or equal to 30 in a range of 500 MHz to 3 GHz. The noise suppression member has a thickness t greater than or equal to 20 μm. The noise suppression member is disposed apart from a conducting wire of the transmission line by a distance greater than 0.05 mm or smaller than or equal to 5 mm.