Reaction method accompanied by production of gas component

A reaction method accompanied by production of a gas component, comprising the steps of:

• supplying a liquid containing at least one raw material compound and a low-boiling compound having a standard boiling point lower than a standard boiling point of the raw material compound to a flow channel;
• heating the liquid to produce a liquid reaction product and a gas component by a reaction of the raw material compound;
• and
• separating a liquid phase containing the reaction product from a gas phase containing the gas component and the low-boiling compound in a gas-liquid separator located outside of the flow channel, wherein the flow channel supplies the gas component only to the gas-liquid separator,
• wherein the flow channel has a specific surface area of 10 m2/m3 or more and less than 1000 m2/m3, and an equivalent diameter of the flow channel is 50 mm or less, wherein the flow channel has only one outlet, wherein the gas component contains at least one selected from the group consisting of water, ammonia, an amine compound, a hydroxy compound and a thiol compound.