A bias circuit includes: a bias supply terminal (800); a parallel capacitor (3) connected at one end thereof to the bias supply terminal (800) and grounded at the other end thereof; and a parallel circuit (3R) connected in parallel with the parallel capacitor (3) and connected at one end thereof to the bias supply terminal (800). Let 2 ‰¤ N. The parallel circuit (3R) includes: a direct-current power supply connection terminal (600); N parallel inductors (2 1 to 2 N ) connected in series with each other between the bias supply terminal (800) and the direct-current power supply connection terminal (600); and N-1 series resonators (9 1 to 9 N-1 ) . Each series resonator (9 1 to 9 N-1 ) includes: a resonant capacitor (7 1 to 7 N-1 ) connected at one end thereof to a connecting point between adjacent parallel inductors; and a resonant inductor (8 1 to 8 N-1 ) connected at one end thereof to the other end of the resonant capacitor (7 1 to 7 N-1 ) and grounded at the other end.
