Abstract: Disclosed herein is a coupler, which is used for discharging a chemical outside a container and includes an internal coupler unit and an external coupler unit. The internal coupler unit includes a mounting part and a coupling pipe. The external coupler unit includes a main housing. Coupling seats are formed in respective opposite ends of the main housing, and a side hole is formed in the main housing. The external coupler unit further includes a hollow rod member, and a hollow cylindrical member. The external coupler unit further includes a subsidiary housing fitted over the hollow cylindrical member, a fluid opening control unit, a pumping means connector, a gas injection means connector tightened into the side hole of the main housing, and sealing caps, which close respective openings of the pumping means connector and the gas injection means connector when not in use.