PURPOSE: To efficiently obtain the titled compound in high conversion rate and selectivity, by circulating a reaction solution of aliphatic ketones, such as acetone, using a liquid ejector, simultaneously sucking unstable ketene gas, absorbing the ketene gas into the reaction solution and continuously carrying out reaction.

CONSTITUTION: A reaction solution of a catalyst, such as naphthalene-1,5- disulfonic acid, and aliphatic ketones, such as acetone, is circulated using a liquid ejector to suck ketene gas, which is then absorbed into the reaction solution and continuously reacted at a temperature of ≥60°C and at least 10°C lower than the boiling point, e.g. 85°C when the conversion rate is 80%, of the reaction solution to afford the aimed compound, such as isopropenyl acetate, in about 80% conversion rate. Although the circulation flow rate of the reaction solution may be determined according to the specifications of the ejector used, a device is preferably adopted so that a circulation flow rate rather higher than the obtained value may be taken to provide a negative pressure of a gas line. Furthermore, continuous operation can be carried out for a long period without operational clogging, etc., by the above-mentioned method for reaction.