An indium phosphide single-crystal body has an oxygen concentration of less than 1×1016 atoms·cm−3, and includes a straight body portion having a cylindrical shape, wherein a diameter of the straight body portion is more than or equal to 100 mm and less than or equal to 150 mm or is more than 100 mm and less than or equal to 150 mm. An indium phosphide single-crystal substrate has an oxygen concentration of less than 1×1016 atoms·cm−13, wherein a diameter of the indium phosphide single-crystal substrate is more than or equal to 100 mm and less than or equal to 150 mm or is more than 100 mm and less than or equal to 150 mm.