With an antenna duplexer having balanced terminals, there has been a problem that the amount of leakage of common-mode signal components in the balanced terminals is large. A balanced high-frequency filter designed to solve this problem comprises a balanced high-frequency element and a phase-shifting circuit which includes a transmission line and placed between output terminals, and which is series resonance circuit having a length set to λT/2 (λT: the wavelength at a frequency in a transmission frequency band) and capable of resonating with common-mode signal components at a predetermined frequency.