To provide a small-size winding part such as a trigger transformer appropriate for downsizing and flattening.

A long-shaped ferrite core 21 having a quadrangle section is formed by an electric insulating material, and a dent part 21c for winding an input coil 22p is formed in the middle of a winding region in this ferrite core 21. Further, U-shaped parts of terminal pieces 23 to 26 are fitted on block parts 21a, 21b at both ends thereof, and also coil ends of the input coil 22p and output coil 22s wound on the ferrite core 21 are held to the terminal pieces 23, 24, 25. Lower-side horizontal side parts of the terminal pieces 23, 24, 25 are soldered directly on a surface of a circuit board in a structure of a trigger transformer.