A piezoelectric element is mounted to a clinch lever for detecting stress-strain generated therein when cutting and clinching leads of an electronic component that has been inserted in corresponding holes formed in a circuit board substrate. A detected voltage d is compared to a threshold voltage s selected from a plurality of threshold voltages preset in the device. When the detected voltage d exceeds the threshold voltage s, the insertion detecting section outputs a signal indicating that the insertion of the leads in the holes has been performed normally.