PURPOSE: To obtain a gravitational acceleration measuring instrument which can accurately measure gravitation acceleration.

CONSTITUTION: A dropping device 101 outputs a start signal and, at the same time, releases an iron ball 108 in response to the operation of a start switch 113 and a noncontact switch circuit 104 outputs a detect signal upon detecting that the iron ball 108 passes through a detection coil 103. A trigger circuit 105 outputs a first trigger signal in response to the start signal and a second trigger signal in response to the detect signal. A timer circuit 106 measures the time until the second trigger signal is generated after the first trigger signal is generated. A personal computer 107 calculates gravitational acceleration based on the distance (an already known value) from the dropping device 101 to the point at which the inductance of the detection coil 103 becomes to have the maximum dynamic value and the time measured by the timer circuit 106.