PURPOSE: To obtain the aimed compound in high purity in producing hydrogen and formaldehyde by dehydrogenating reaction of methanol, and by using both ultrafine particle metal catalyst having a specific average particle diameter and an alkali metal alcoholate.

CONSTITUTION: Methanol is dehydrogenated in the presence of preferably 0.2W10wt% based on methanol of fine particles of one or more metals selected from copper, iron, silver, nickel and cobalt having ≤1,000 average particle diameter and 0.4W150wt% alkali metal alcoholate preferably at 60W150°C to give high-purity hydrogen and formaldehyde useful in the field of chemical industry, electronic material industry, precision metal industry, etc. Addition of a high-boiling solvent to the reaction system can raise the reaction temperature to a high temperature readily without increasing the pressure of the reaction system and in turn can promote the reaction.