There is provided a method of manufacturing coalesced resin particles for obtaining coalesced resin particles by coalescing aggregated resin particles in a grain boundary-free state in a short period of time while keeping a grain size distribution within a narrow range. In a coalescence process, a slurry of aggregated resin particles is flowed through an inside of a pipe under predetermined heating and pressurizing conditions. In a before-cooling decompression process, a slurry of coalesced resin particles flowing through the inside of the pipe in a heat and pressure-applied state is subjected to pressure reduction before it is cooled down to a predetermined temperature in a cooling process. Then, in a decompression process, a coalesced resin particle slurry that has been cooled in the cooling process while being flowed through the inside of the pipe is decompressed to an atmospheric pressure.