Cleaning method, method of manufacturing semiconductor device, substrate processing apparatus and recording medium

A cleaning method includes: providing a process container in which a process of forming a film on a substrate is performed; and removing a deposit including the film adhered to the process container by supplying a cleaning gas into the process container after performing the process. The act of removing the deposit includes generating a mixture gas of a fluorine-containing gas and a nitrosyl fluoride gas as the cleaning gas by mixture and reaction of the fluorine-containing gas and a nitrogen monoxide gas in a mixture part and supplying the mixture gas from the mixture part into the process container after removing exothermic energy generated by the reaction.