PURPOSE: To make possible the measurement of high accuracy on a small size structure that is simple and superior in portability by allowing a member to be detected having the specified length vertically to freely fall to measure gravitational acceleration on the basis of a falling distance and falling time.

CONSTITUTION: A thimble 13c of a micrometer 13 is rotated to vertically move a falling object 11 to be measured having the specified length L so as to adjust to a standard position. For instance, the edge part 11a of the object 11 is adjusted so as to be positioned just before the detection position of a photointerrupter 14. A push switch 12b is pushed to interrupt exciting current of an electro-magnet 12a to allow the object to fall and, when the object 11 interrupts light from an LED 14a with the use of a timer 16, namely, falling time (t) showed as the pulse width of the output voltage CI of an amplifier 15 is measured. Next gravitational acceleration (g) is calculated with the use of g=2L/t2 on the basis of the length L of the time (t) and the object 11 in an operation circuit 17 is displayed in a display 18.