To provide a conversion device acquiring rotational energy by efficiently utilizing pressure of wind or flowing water or the like.

Fig.1 is a perspective view when three blades 4 are arranged. The bade 4 receives a rotational force around a center axis 8 because of pressure of wind or a fluid. A roller 3 disposed at a blade end is in contact with the groove 2 of a guide plate 1 and the positions of the blade ends at the respective positions are restricted. Thus, the blades 4 themselves are able to maintain optimal angles with respect to the direction of the wind or the fluid.