PURPOSE: To surely insert cores and rings without applying stress to the glass tube of each reed switch by guiding lead wires at portions where the cores and the rings are inserted, while securing the lead wires at each insertion portion independently of the conveyor of assembling jigs.

CONSTITUTION: While a reed switch 1 is being held an assembling jig 21 is conveyed to the place of an assembling jig 22 by an intermittent conveyor 10. An assembling device guides the reed upper ends of reed switches 1 on the assembling jigs 21, 22, 23 by means of guide plates 19, 20 and inserts two magnetic cores 2 on a parts feeder 12 into the reed switches 1 of the jigs 22, 23 by means of a pick-and-place unit 15 while varying pitches. In this case, the upper end of each lead wire into which the core is inserted is not dependent on the positioning accuracy of the assembling jigs but is positioned relative to the pick-and-place unit, thus ensuring insertion of the cores. After insertion the guide plates 19, 20 are oscillated so that the cores located on the plates 19, 20 drop onto a plate 5.