PURPOSE: To contrive to conserve the energy of a hydrogen sulfide recovery apparatus by automatically controlling the recirculation amount of an absorbing liquid and the steam amount of a regeneration tower, by controlling the recirculation amount of the absorbing liquid and the heating amount of the regeneration tower by calculating the hydrogen sulfide amount in supply gas and the outlet gas of the regeneration tower.

CONSTITUTION: Hydrogen sulfide-containing hydrogen gas is supplied to a first absorbing tower 1 while hydrogen sulfide-containing OFF-gas is supplied to a second absorbing tower 2. The absorbing liquid from the tower 1 is returned to a recirculation passage L1 and the absorbing liquid from the tower 2 is also returned to L1 while the liquid after regeneration is returned through L2. An inlet stock gas flow amount is calculated from an outlet gas flow amount while the H2S-amount in the stock gas is calculated and the objective value of the flow amount of the absorbing liquid is set from the calculated values and a solution load formula. The value obtained by multiplying each of the values of flow amount detectors F1WF3 by the ratio of the absorbing liquid and steam is used as an objective value to perform the optimum control of the steam amount.