The object of the invention is to provide a method for producing (meth)acrolein or (meth)acrylic acid by gas phase catalytic oxidation reaction, which can perform smooth temperature control of the heat medium, can prevent hot spot effectively and can be handled easily, and an apparatus. The invention are a method for producing (meth)acrolein or (meth)acrylic acid by carrying out gas phase catalytic oxidation reaction of propane, propylene, isobutylene or (meth)acrolein with an oxygen-containing gas using an inorganic salt as a reaction temperature adjusting heat medium, characterized in that the material of a gland packing member which seals body part of a regulating valve arranged on a heat medium feeder and controlling supply and circulation velocity of the heat medium and a rotation axis that interfits to the body part, in such a manner that they can perform sliding, is a mica-based material, and a production apparatus.