To provide a hardener feeder in which hardener supply can be regulated automatically depending on the variation in the delivery rate of a spraying material when a refractory material, or the like, is sprayed by a wet spray method.

The hardener feeder comprises a hardener supply pump 23, a first detector 24 for detecting the instantaneous supply of hardener, second or third detector 12, 11b for detecting the instantaneous supply of a spraying material, and a hardener pump 23 controller 31 connected with respective detectors 24, 12, 11b, wherein the hardener pump 23 is controlled depending on the variation in the instantaneous supply of the spraying material to add a constant rate of hardener.