Process for producing (meth)acrolein and/or (meth)acrylic acid

A method for producing (meth)acrolein and/or (meth)acrylic acid by subjecting isobutylene and the like or propylene to a vapor-phase catalytic oxidation with molecular oxygen in the presence of a solid oxidation catalyst in a tubular type of fixed bed reactor, wherein a temperature of a hot-spot zone is sufficiently controlled and (meth)acrolein and (meth)acrylic acid are produced with a high yield. A method for producing (meth)acrolein and/or (meth)acrylic acid by passing a raw material gas comprising isobutylene and the like or propylene and oxygen through a catalyst layer in a tubular type of fixed bed reactor which is filled with a solid oxidation catalyst, which includes passing a gas containing isobutylene and the like or propylene in a concentration lower than that of the raw material gas, and oxygen through the catalyst layer for a period of one hour or more prior to passing the raw material gas through the catalyst layer.