A compound semiconductor device includes: a flexible part; a first nitride semiconductor layer above a surface of the flexible part, the first nitride semiconductor layer including a first polar plane and a second polar plane intersecting the surface; a second nitride semiconductor layer in contact with the first nitride semiconductor layer on the first polar plane, a lattice constant of the second nitride semiconductor layer being different from that of the first nitride semiconductor layer; a third nitride semiconductor layer in contact with the first nitride semiconductor layer on the second polar plane, a lattice constant of the third nitride semiconductor layer being different from that of the first nitride semiconductor layer; a first ohmic electrode above an interface between the first nitride semiconductor layer and the second nitride semiconductor layer; and a second ohmic electrode above an interface between the first nitride semiconductor layer and the third nitride semiconductor layer.