A vibration type force detector in which the vibration string is made of a platinum-based nickel-containing alloy. The magnitude of a force to be detected is obtained through the measurement of a natural vibration frequency of a string vibrating with the force loaded thereto. However, the force detector using a Pt-Ni alloy vibration string based on the invention makes it possible, for the first time, to apply a vibrational type force detector to a precision measurement of force or weight. Measurement with an accuracy of 10-5 is made possible by the present invention.