A process for producing a carbonic acid diester, which comprises carrying out a reaction in a vapor phase of an alcohol, carbon monoxide and oxygen in the presence of a catalyst in a fluidized-bed reactor so that an oxidative carbonylation of the alcohol occurs, thereby obtaining a carbonic acid diester, wherein a heat of reaction is removed by the latent heat of vaporization of the alcohol as a raw material. In the process, for example, either at least part of the alcohol may be directly fed in liquid phase into the fluidized bed or cooling pipes are disposed in the fluidized bed and at least part of the alcohol is introduced in liquid phase into the cooling pipes as a heat transfer medium so that the liquid alcohol is vaporized and fed into the fluidized-bed reactor. Carbon monoxide may be introduced together with the liquid alcohol into the cooling pipes. A process of high energy efficiency realizing an effective utilization of a heat of reaction and an apparatus there for are provided in the production of a carbonic acid diester in a vapor phase with the use of a fluidized-bed reactor.