A multiplexer includes a transmit filter circuit, a receive filter circuit, and an additional circuit connected in parallel with a portion of the transmit filter circuit. The transmit filter circuit includes series resonators on a signal path connecting a common terminal and a first terminal, and parallel resonators on the signal path between a node and ground. The series resonator closest to the first terminal includes split resonators. The additional circuit includes a capacitor and a resonator group. The resonator group includes IDT electrodes side by side in the direction of acoustic wave propagation. A first end of the resonator group is connected to the common terminal with the capacitor interposed therebetween. A second end of the resonator group is connected to the signal path between two of the split resonators such that no capacitor is interposed between the second end and the signal path.