PURPOSE: To measure accurately and automatically an electroless plating speed and to control plating by providing an electric circuit of a specified pattern by a conducting treatment on an insulating material, measuring the electric resistance of the circuit in an electrolytic plating liquid and calculating the plating speed.

CONSTITUTION: A metal such as Cu or Ni is electroless-plated on the surface of the insulating material 7 consisting of glass, ceramic or various other films by which the material 7 is made conductive. The electric circuit part 6 for resistance measurement having the specified pattern is formed by using a plating resist material in this stage and electrodes 5 for measuring the resistance values are attached to the ends of the circuit part 6 to obtain a plating speed sensor 2. The sensor 2 is immersed into a plating cell 1 of the electroless plating device and is connected via the electrodes 5 to a resistance value measuring mechanism 3 by which the resistance value is measured. The electroless plating speed in the plating cell 1 is automatically and on time measured with good accuracy by a calculator 4 from the measured value by which the plating quality is made constant.