The electrical conductivity and X-ray diffraction measurements were performed for a highlyconductive halogen-bridged binuclear-metal mixed-valence complex (the so-called MMX chain), Pt-2(C2H5CS2)(4)I, under high pressure up to 2.5 GPa. The complex exhibited pressure-induced metal-semiconductor-metal transitions at 0.5 and 2.1 GPa. The Xray diffuse scatterings were observed at k = n+0.5 (n: integer) under ambient pressure, which are derived from the charge-density wave (CDW:center dot center dot center dot Pt-2-Pt2+center dot center dot center dot I-Pt3+-Pt3+-I center dot center dot center dot) fluctuation in the MMX chain. Above 0.5 GPa, where the pressure-induced metal-semiconductor transition occurred, these scatterings disappeared. The electronic phases under high pressure (P) were found to be attributable to the metallic averaged-valence state (AV: -Pt2.5+-Pt2.5+-I-Pt2.5+-Pt2.5+-I-) with CDW fluctuation of P < 0.5 GPa, semiconducting charge-polarization state (CP:center dot center dot center dot Pt2+-Pt3+-I center dot center dot center dot Pt2+-Pt3+-I center dot center dot center dot) of 0.5 < P < 2.1 GPa, and metallic AV state of P > 2.1 GPa. The electronic state Of Pt-2(C2H5CS2)(4)I is very sensitive to pressure, which implies that the phase competition among the CP, CDW, and AV phases is present in the MMX chain.