To provide a chemical-feed controller which is capable of taking a rapid and adequate measure according to a slime production state even for a water system at a remote place and surely preventing a slime fault.

A tendency to slime production of the water system is detected by a slime adhesion tester 8 having a torque meter 10. This detection signal is monitored in a host computer 20 through a communication circuit 14. When the need for a change of chemical-feed conditions arises, a signal for changing the chemical-feed conditions is sent from the host computer 20 to an on-the-spot microcomputer 11.