Abstract: The temperature distribution of a heating medium in the reactor is allayed and the occurrence of hot spots is repressed. In a shell-and-tube type reactor provided with donut type and disc type baffle plates, reaction tubes are disposed even in the holes formed in the donut type baffle plates and an empty space devoid of a configuration of the reaction tubes is formed at the center of the shell. According to this invention, (meth)acrylic acid and/or (meth)acrolein can be produced at a low energy by catalytic gas phase oxidation of propylene- or isobutylene-containing gas.