A multiplexer includes: a first filter connected between a common terminal and a first terminal; a second filter connected between the common terminal and a second terminal, and having a passband lower in frequency than a passband of the first filter; and a resonant circuit including: a first inductor and a capacitor connected in series between a first end and a second end of the resonant circuit, the first end being coupled to a node at which the common terminal diverges into the first filter and the second filter, the second end being coupled to the first filter, and a second inductor connected in parallel to the first inductor and the capacitor between the first end and the second end, wherein the passband of the first filter is higher in frequency than an antiresonant frequency of the resonant circuit.