PURPOSE: To make it possible to simply calculate non-steady air force, by vibrating only one blade in a cascade while measuring the non-steady fluid forces of said blade and the adjacent blades.

CONSTITUTION: A wind is blown out at a flow speed V from an emitting port A to be acted on a blade lattice and a vibration blade O is vibrated at bending displacement (h). If lift and moment are respectively measured in this state, the next non-steady fluid force can be measured. In this case, by measuring L1o, M1o from the vibration blade O, L1p, M1p from a stationary blade P and L1s, M1s from a stationary blade S while vibrating the vibration blade O at twist displacement α, six non-steady fluid forces of L2o, M2o from the vibration blade O, L2p, M2p from the stationary blade P and L2s, M2s from the stationary blade S are calculated.