An object is to maintain the hydrogen sulfide concentration in rearing water at a constant value without measuring the hydrogen sulfide concentration in the rearing water. The present invention includes: a water tank 10 that stores rearing water W leaving a gas phase at an upper part; a gas sensor 50 to detect hydrogen sulfide gas concentration in the gas phase G; and a hydrogen sulfide supplying means F to supply hydrogen sulfide to the rearing water W based on a detection signal output from the gas sensor 50 so as to maintain a hydrogen sulfide concentration in the rearing water W at a predetermined value.