PURPOSE: To attempt automation and speed-up of work, according to a method wherein a magnetic body is separated from a magnetic chuck securely at a preset position, even through it is light by electrifying a magnetic chuck with AC exciting current of gradually increasing frequency, and it is set in the assigned position.

CONSTITUTION: Respective arms 3W5 of a robot 1 are controlled to apply AC exciting current of fixed frequency to a magnetic chuck 6 so as to adsorb pin P to the chuck 6 and the pin is set in an insertion hole 8b on an assembly stand 8 from above a work table 7. At this point of time, an OFF-signal for AC exciting current is given to a delay circuit from a controller and AC exciting current for demagnetization with gradually increasing frequency is arranged to flow for a specified period according to the above OFF signal, and perfect demagnetization takes place at the assigned time of demagnetization. Accordingly, assembly work for P pin can be carried out precisely, securely and smoothly, thus automation and speed-up of work can be attempted.