PURPOSE: To form the miniature and low-cost operation mechanism to extract the square root by using the rigid beam and the plate spring, and thus to apply the mechanism to the air measurement instrument or the like.

CONSTITUTION: Input F1 is applied to one end of rigid beam 1, and the other end is supported rotatably at fulcrum O1. The one end of rigid beam 2 is fided to the other end of beam 1, and the other end is connected to one end of plate spring 3. Plate spring 3 is provided in parallel to one side of beam 2, and output F2 is drawn out from the other end of plate spring 3. Spring 3 is deformed by being bent with connection point O2 to beam 2 used as the fixed end. Thus, Eq. (I) is atisfied if the balance is kept between F1 and F2, and Eq. (III) is obtained from Eq. (I) plus (II) which is obtained when the spring characteristics is linear. Accordingly, the square root of F1 can be obtained by measuring output F2, and the square of the input is obtained as the output when the input and output are reversed to each other. Thus, operation mechanism can be applied to the air measurement instrument or the like.