This paper describes a variable torque transmission control using a magnetic fluid which is influenced by a magnetic field. A nonmagnetic disk rotates inside a case made of iron and the magnetic field is induced by a magnetic coil. When an electric current is applied to the coil, the magnetic fluid is shifted to the outer area of the rotating disk, and a torque is transmitted via the viscous friction of the magnetic fluid between the disk and the case. The basic characteristics of this magnetic fluid coupling were examined experimentally. It is confirmed that the output torque can be controlled by electric signals. The values of output torque depend on the amount of magnetic fluid when the input signal is turned on or off.