A hydrogen sulfide gas production plant system, comprising: a plurality of systems of hydrogen sulfide gas production plants provided with at least a reaction facility that generates hydrogen sulfide gas from sulfur and hydrogen gas, a plurality of cooling facilities that cool the generated hydrogen sulfide gas, and a sulfur recovery facility that recovers sulfur contained in the hydrogen sulfide gas, the hydrogen sulfide gas production plant system that: the hydrogen sulfide gas production plant of each system is provided with a first supply pipe that supplies the hydrogen sulfide gas from which sulfur has been recovered in the sulfur recovery facility to a processing plant that uses hydrogen sulfide gas, and a second supply pipe that is branched at a predetermined point in the first supply pipe and supplies the hydrogen sulfide gas from the sulfur recovery facility to the processing plant; the first supply pipe has a concentration meter that is provided on the sulfur recovery facility side than the predetermined branch point and measures the concentration of the hydrogen sulfide gas; and the first supply pipe and the second supply pipe each have an ON/OFF valve that is provided on the processing plant side than the predetermined branch point and turns ON/OFF the supply of the hydrogen sulfide gas to the processing plant through the supply pipe. a plurality of systems of hydrogen sulfide gas production plants provided with at least a reaction facility that generates hydrogen sulfide gas from sulfur and hydrogen gas, a plurality of cooling facilities that cool the generated hydrogen sulfide gas, and a sulfur recovery facility that recovers sulfur contained in the hydrogen sulfide gas, the hydrogen sulfide gas production plant system that: the hydrogen sulfide gas production plant of each system is provided with a first supply pipe that supplies the hydrogen sulfide gas from which sulfur has been recovered in the sulfur recovery facility to a processing plant that uses hydrogen sulfide gas, and a second supply pipe that is branched at a predetermined point in the first supply pipe and supplies the hydrogen sulfide gas from the sulfur recovery facility to the processing plant; the first supply pipe has a concentration meter that is provided on the sulfur recovery facility side than the predetermined branch point and measures the concentration of the hydrogen sulfide gas; and the first supply pipe and the second supply pipe each have an ON/OFF valve that is provided on the processing plant side than the predetermined branch point and turns ON/OFF the supply of the hydrogen sulfide gas to the processing plant through the supply pipe. the hydrogen sulfide gas production plant of each system is provided with a first supply pipe that supplies the hydrogen sulfide gas from which sulfur has been recovered in the sulfur recovery facility to a processing plant that uses hydrogen sulfide gas, and a second supply pipe that is branched at a predetermined point in the first supply pipe and supplies the hydrogen sulfide gas from the sulfur recovery facility to the processing plant; the first supply pipe has a concentration meter that is provided on the sulfur recovery facility side than the predetermined branch point and measures the concentration of the hydrogen sulfide gas; and the first supply pipe and the second supply pipe each have an ON/OFF valve that is provided on the processing plant side than the predetermined branch point and turns ON/OFF the supply of the hydrogen sulfide gas to the processing plant through the supply pipe.