A separation membrane (10) of the present disclosure includes: a separation functional layer (30) composed of a polyamide containing, as a monomer unit, at least one selected from the group consisting of piperazine and a piperazine derivative; and a coating (40) covering the separation functional layer (30) and containing a polymer having a repeating unit represented by the following formula (1). In the formula (1), N+ is a nitrogen atom constituting a quaternary ammonium cation, and R1 and R2 are each independently a substituent containing a carbon atom bonded to the nitrogen atom.