Multimolecular-micelle formation is investigated by means of light scattering for poly(methyl methacrylate)-graft-polystyrene with low grafted-chain density in a dilute solution of mixed selective solvent of acetonitrile and acetoacetic acid ethyl ether. Molecular weights of the poly(methyl methacrylate) (PMMA) backbone and the polystyrene (PS) branch are about 5.6 x 10(6) and 9.2 x 10(3), respectively, and the grafted-chain density is 13 wt % PS. The mixed solvent is a marginally-good solvent to PMMA and is a nonsolvent to PS. Time evolutions of apparent molecular weight M(app), radius of gyration R(gapp), and hydrodynamic radius R(happ) are measured in the course of micellization after quenching from the unimer region to the micelle region. Observed M(app) dependences of R(gapp), R(happ), and R(gapp)/R(happ) demonstrate the following features of multimolecular-micelle formation. Unimolecular micelles, which are made of a few linearly-connected flowers with small cores of associated PS branches and petals of PMMA backbone, are associated with each other by primarily connecting at the ends of respective end-flowers to form multimolecular micelles of the flower-connecting type. An analysis with a worm-like chain model reveals that the multimolecular micelle is fairly rigid, having the contour length of more than several hundreds of nanometers.