IrTe2 has a trigonal CdI2-type structure which consists of stacked layers of triangular Ir lattices sandwiched between Te layers with octahedral coordination. Pt-doping prevents a first-order structural phase transition to a monoclinic structure at 250 K, and induces superconductivity at 2.8 K. When superconductivity is exhibited, it competes with the structural phase transition. We performed single-crystal X-ray diffraction to investigate the relationship between superconductivity and the structural change by Pt-doping. Pt was substituted at the Ir site, and was not likely to be intercalated between the Te layers. With increasing Pt- doping content, the degree of the distortion of the IrTe6 octahedron increased and the thickness of the IrTe2 layer decreased although the Ir-Te distance hardly changed.