A multiplexer (1) used in a communication device (5) includes an antenna (21) for a first frequency band group including 5GNR and an antenna (22) for a second frequency band group and includes a filter (12) for a first communication band and a filter (13) for a second communication band. The second frequency band group is higher than the first communication band, the second communication band is lower than the first communication band, the filter (12) includes a resonant circuit (31), an inductor (L1) connected to a node (n1) in a series arm path, and an inductor (L2) magnetically coupled with the inductor (L1).