Dynamic birefringence and viscoelasticity of a diblock copolymer micellar solution were measured in order to clarify the molecular origin of viscoelastic response of the macrolattice structure formed by micelles. The complex strain-optical ratio changed its sign with angular frequency omega and exhibited very complicated omega dependence, suggesting that the stress emerged/relaxed through several mechanisms. With an assumption of the stress-optical rule for each mechanism, the complex shear modulus was separated into four components corresponding, from high to low omega, to the reorientation of corona chains, reorientation of core chains, deformation of core, and deformation of the micellar lattice. Values of the stress optical coefficients for respective components lent support to these assignments.