In the related art, no consideration is given to a configuration of a deformation detecting device, an installation place or an installation method for the measurement target. Therefore, there is provided a deformation detecting device including a film-like elastic body which has a first surface to be adhered to a measurement target and a second surface opposite to the first surface, and in which the second surface has at least one set of a recess portion and a projection portion in a first direction in a state where the first surface is adhered to the measurement target before deformation; a first electrode formed in a region of the recess portion of the second surface; a second electrode formed in a region of the projection portion of the second surface; a film-like piezoelectric body which has a uniform thickness and has a third surface disposed along the second surface of the elastic body and a fourth surface opposite to the third surface, and of which a shear modulus of elasticity is higher than that of the elastic body; a third electrode formed in a region of the fourth surface opposite to the first electrode; and a fourth electrode formed in a region of the fourth surface opposite to the second electrode.