A mixing device used in a fluidized catalytic cracking apparatus which mixes feed and a catalyst includes a cylindrical reaction container which supplies a catalyst in a vertical direction; a plurality of feed injection nozzles arranged along an outer circumference of the reaction container; and a catalyst flow regulator which is provided in the reaction container and regulates a flow of the catalyst in the vicinity of the feed injection nozzles. The catalyst flow regulator has no feed supply function and forms a catalyst moving bed having a hollow tubular shape which is coaxial with the reaction container in the vicinity of the feed injection nozzles. The catalyst flow regulator can effectively prevent backward flow of injected fuel. Although the mixing device has a simple structure, it has a high cracking rate and maintenance of the fluidized catalytic cracking apparatus can be performed easier.