In order to clarify the quantum spin contraction in the limited-size organic spin systems, we have directly determined the sigma and pi spin densities on the C-13-isotope labeled divalent carbon site of an organic high-spin molecule, 4-(diphenylmethylene)-4’-[m-phenylenebis(phenylmethylene)] ether 1. 1 is the most simple model compound for topologically controlled ferrimagnetic spin ordering. The magnitude of the spin density on the divalent carbon site in the diphenylmethylene moiety of 1 is almost one-half of that of diphenylmethylene molecule. This finding gives a direct evidence of the spin contraction expected as a quantum effect on the limited-size ferrimagnetic spin system. We have also carried out the theoretical calculation of the spin-densities, spin-energies, and spin functions for the ferrimagnetic spin chain systems (-S-A-S-B-S-A-S-B...., S-A not equal S-B) with different chain lengths by the exact numerical calculation. number of the repeating unit -S-A-S-B-, the spin contraction has been recovered. The size dependency of the quantum spin contraction is discussed based on the theoretical calculation.