FIG. 6 is an explanatory drawing showing an equivalent circuit of the high frequency filter 1. In FIG. 6, a connection portion 200 connected to a port (1) corresponds to the coaxial line 12A shown in FIG. 3, and a connection portion 201 connected to a port (2) corresponds to the strip line 10. A coupled line 202 and a coupled line 203 correspond to the coaxial line 12B. A capacitance C1 corresponds to the capacity formation section (1), a capacitance C2 corresponds to the capacity formation section (3), and a capacitance C3 corresponds to the capacity formation section (2).

The electrical length of the coupled line 202 is 90 degrees or less at the center frequency (cutoff frequency) of the stopband where the transmission of signals is rejected in the high frequency filter 1, and is d1 shown in FIG. 3. The electrical length of the coupled line 203 is 90 degrees or less at the cutoff frequency, like that of the coupled line 202, and is d2 shown in FIG. 3. The characteristic impedance of the coupled line 202 and the characteristic impedance of the coupled line 203 are determined by the spacing dB shown in FIG. 3.