To provide a small and low-cost signaling transformer for switching power supply apparatus, which obtains proper and stable inductance and magnetic coupling adequate to the type of the communicated signal or usage, and to provide a switching power supply apparatus.

A plurality of coil patterns 24a and 24b formed on a substrate 12 in a concentric pattern, and a core 14 arranged in the vicinity of the coil patterns 24a and 24b, are provided. The core 14 consists of a bottom plate 18, and a pair of legs 20a and 20b provided so as to stand in a vertical direction to the bottom plate 18 from right and left side ends of the bottom plate 18. The legs 20a and 20b, which become paired, are inserted into a penetrating hole 32 and a notch 34 formed in the coil center and the coil outside of the plurality of coil patterns 24a and 24b arranged in the concentric pattern, respectively. A magnetic circuit of the core 14 is formed via a space in the core 14 and a space between the legs 20a and 20b, which become paired.

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