A force sensor based method to detect the instant of needle puncture to the layers of tissues is proposed. A set of needle and sheath attached to a pair of coaxial force sensors was used to separately measure the cutting force at the needle tip and the sidewall friction. Change of the force profile was observed and marked at the instant of the puncture, and robustly eliminated artifacts caused by body motion such as the respiratory or cardiac motion. The agreement between the subjective feeling of a skilled surgeon and the sensor was good. In several cases the sensor detected the puncture even when the surgeon could not clearly identify it. It was suggested that the sensor is potentially more sensitive than skilled professionals.