Quantization of motion of a rigid body and its extension to the relativistic form are attempted here. The special theory of relativity is believed that it rules the phenomena in the macroscopic world. But, so far, we do not know the rule which governs the microscopic world as the interior of an elementary particle. Here we assume that the internal space of an elementary particle is Euclidean. The field equation, however, has the relativistically invariant form so that the expectation values of observable quantities become relativistically covariant. The condition that the time components of an internal angular momentum have zero expectation values in the rest system leads to the general linear equation derived by Bhabha for elementary particles with arbitrary spins. When interactions are absent, the solutions of the field equations are obtained and quantization of the field of a rigid sphere is done.