To provide a method of inhibiting vinyl ether group-bearing (meth) acrylic ester monomers from causing undesired polymerization on the heat transfer surface simply and economically when vinyl ether group-bearing (meth) acrylic ester monomers are heated.

A solution including vinyl ether group-bearing (meth)acrylic ester monomers and polymerization inhibitors or a solution including vinyl ether-group bearing (meth)acrylic ester monomers, polymerization inhibitors and basic compounds is sucked up from the lower part of the agitation blades by the centrifugal force of the agitation blades fixed to the rotary shaft and sprayed down from the upper part of the agitation blades whereby almost all of the heat transfer surface are substantially wetted with the solution.