Using mainly numerical methods, we investigate the ground-state phase diagram of the S = 2 quantum spin chain described by H = j (S Quantum spin chain systems have been attracting increasing attention in recent years because they provide rich physics even when models are rather simple. The most well-known example may be the existence of the Haldane phase 1, 2) in integer spin chain systems only with isotropic nearest-neighbor (nn) interactions.In this study, using mainly numerical methods, we explore the ground-state phase diagram of the S = 2 quantum spin chain described by the Hamiltonianwhere S α j (α = x, y, z) is the α-component of the S = 2 operator at the j-th site, and ∆ and D are, respectively, the XXZ anisotropy parameter of the nn interactions and the on-site anisotropy parameter. Hereafter, we denote the total number of spins in the system by N , assumed to be even, and the z component of the total spin by M = j S z j . The ground-state phase diagram on the ∆-D plane of the same Hamiltonian in the S = 1 case was discussed by Schulz 3) and den Nijs and Rommels, 4) and numerically determined by Chen et al. 5) In the present S = 2 case, Schulz 3) discussed the ground-state phase diagram with six phases obtained by the bosonization method; the phases are, in our terminology, the ferromagnetic (FM) phase, the Néel phase, the XY 1 phase, the XY 4 phase, the Haldane phase and the large-D (LD) phase. The XY 1 state is characterized by the power decay of * E-mail address: tone0115@vivid.ocn.ne.jp Figs. 1(a) and (c), respectively. About twenty years ago, Oshikawa 6) predicted, in S ≥ 2 integer quantum spin cases, the existence of the intermediate-D (ID) phase, the valence bond picture of which is depicted in Fig. 1(b). Figure 2(a) is an interpretation of Oshikawa's prediction by Aschauer and Schollwöck 7) in the S = 2 case. On the other hand, carrying out the density-matrix renormalization-group (DMRG) calculation, Schollwöck et al. 8,9) and Aschauer and Schollwöck 7) proposed the phase diagram in Fig. 2(b) and concluded the absence of