To provide an operation controller for a viscous fluid mixer wherein if a safety cover is not covered on a mixer barrel, operation of the mixer can not be started, and when the safety cover is detached, the operation is stopped.

An operation circuit 20 wherein a starting push button switch 10, a stopping push button switch 11 and a limit switch 1 which turns ON when a safety cover is covered on a mixer barrel are in series provided, is connected to a power circuit 29 equipped with a plus socket 17 for connecting a motor of a viscous fluid mixer wherein raw material and water which are kneaded in a mixer barrel by driving of the motor to prepare viscous fluid. A contactor 22 is incorporated between an operation circuit 20 and a power source circuit 29. The contactor 22 has an electromagnetic coil 28 and a plurality of contact points 23, 24 and 27 turning ON by excitation of the electromagnetic coil. The electromagnetic coil 28 is connected to the operation circuit 20, and contact points 24 and 25 are made opening and closing contact points of the power circuit 24. An auxiliary circuit 21 connected to the operation circuit 20 is connected to the contact point 27.