To provide an interference preventing circuit for a high frequency multilayer substrate which can prevent continuous propagation of a high-frequency signal on control wiring or power supply wiring and thereby can prevent interference on a high-frequency circuit from the control wiring or power supply wiring in the high-frequency multilayer substrate.

On control wiring or power supply wiring 3, a first branch point C is provided and second and third branch points A and B are provided to both sides in the wiring direction of the first branch point C. The length of each line 7a and 7b between the first branch point C and the second and third branch points A and B is set to a quarter of the wavelength of the fundamental waves of a high frequency signal generated by a high-frequency circuit 2. An open stub 8 having a line length equal to a quarter of the wavelength of the fundamental waves of the high-frequency signal is connected to the first branch point, while means (6a and 6b) to which one ends of resistive elements 5a and 5b are connected, respectively and which ground the other ends of the resistive elements, with respect to the high frequency signal, are connected to the second and third branch points A and B, respectively.