To improve a transmission efficiency in a low pass while ensuring an attenuation value under a coupled state in the case of a high pass higher than a specified level and to reduce unnecessary signals and noises.

A pulse transformer has a closed magnetic-circuit core 3 mechanically forming a closed magnetic circuit without an opening, a primary winding 4 and a secondary winding 5 wound at the separate places of the core 3 respectively while using the core 3 as a winding shaft and a coupling control core section 6 being arranged between the primary winding 4 and the secondary winding 5 and controlling the capacitive coupling of the winding 4 and the winding 5 in a high-frequency band higher than the specified level.