Dynamic birefringence and viscoelastic measurements of bottlebrush-like polystyrene polymacromonomer were conducted over a wide frequency region covering from the glass-to-rubber transition zone to the flow zone in order to discuss effects of highly branched structure on polymer chain dynamics. Strain-induced birefringence at high frequencies was negative, similarly to linear polystyrenes, while it was positive in the flow zone, indicating the main chain segment has positive optical anisotropy. By using the modified stress-optical rule (MSOR), the complex modulus was decomposed into two components, main chain and branch components. The dynamical stiffness of main chain (number of repeating units per viscoelastic segment) was found to be approximately 10 times larger than that for linear polystyrenes. The cooperative motion of the side chains originated by the repulsive interaction between the branches was strongly suggested.