Provided is a method for producing fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride ((CF3)2CHCOF), which are useful as dry etching gases etc., safely and inexpensively with high purity.According to the method in which 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether is pyrolyzed in a gas phase in the presence of a catalyst, the desired fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride can be obtained with high selectivity and high conversion of the starting material by a simple process in which a pyrolysis reaction is performed in a gas phase using the inexpensive starting material.