PURPOSE: To enable the sure detection of the defective insertion of a lead pin by a method wherein a chuck pawl and a stopper are provided, and the detection is made to find if the insertion of the lead pin is defective or non-defective depending on the distance of descent of the chuck to the reference distance of the chuck which is set considering a specified distance.

CONSTITUTION: A chuck pawl 16 capable of opening or closing freely, which holds a lead pin 30 of an electronic component 25 from its sides, and a stopper 33 formed into a solid structure with the chuck pawl 16, which is positioned at a specified distance A above the component main body 25, are provided. When the tip of the pin 30 can not be inserted bearing on the surface of a printed wiring board 31, an inserting head 2 is made to stop descending, because the torque of a motor 6 is so controlled as to be small enough not to bend the pin 30. That is, when the distance l of descent is smaller than a distance B, a control section 10 detects that the insertion is defective. By this setup, the defective insertion of a lead pin can be surely detected.