To provide a power and ammonium sulfate cogeneration system combined with a coal gasification process that can reduce the production cost of ammonium sulfate and can alder the proportion between the production of ammonium sulfate and the electric power generation.

Calcium sulfate 3 and coal 1 are mixed and the mixture is fed into the lower-step room of the two-stepped coal-gasification chamber 19 to increase the concentration of hydrogen sulfide in the formed gas. The temperature of the upper step inside the gasification chamber 21 is controlled to raise the concentration of the ammonia in the produced gas to produce ammonium sulfate from the ammonia and hydrogen sulfide in the synthetic column 31. The carbon monoxide and hydrogen in the formed gas are used as a fuel for the gas turbine. The hydrogen sulfide and ammonia from the coal gasification chamber 19 are converted to ammonium sulfate in the synthetic column 31 thereby reducing the cost. The feed ratio of the calcium sulfate to the coal is adjusted to control the production ratio of ammonium sulfate to electric power whereby the operation efficiency of the entire plant is increased.