Atomic force microscopes (AFM) have been used to measure the strength of adhesion of photoresist patterns which generally collapse during rinsing with water in the development process. We suggest how to measure the collapsing force of the photoresist patterns using an AFM in which a lateral force microscope (LFM) is engaged to determine the tip load at the moment of pattern collapse. The AFM tip was precisely positioned in the space between the patterns in non-contact mode and then scanned in contact mode to the collapse patterns. Loads F for collapse on a scale of nanonewtons (nN) were calculated from the signal of the position-sensitive photodiode. To investigate the variation of the collapsing load for different lengths of patterns, an AFM tip was also used to fabricate patterns with an appropriate length. Our method for measuring the strength of adhesion of photoresist patterns would enable an AFM to be applied to test this property for photoresists.