In a method for producing hydrogen and carboxylic acid, a primary alcohol of 1 to 7 carbon atoms and water are reacted by being continuously introduced into a flow reactor packed with a solid catalyst consisting of an alloy of ruthenium and tin on a support and passed through the reactor under temperature and pressure conditions at which the water assumes a gaseous state. This method enables hydrogen and carboxylic acid to be produced in a high yield or at a high purity from a primary alcohol and water in a short time and by simple operations.