A polishing composition includes a copolymer and an abrasive. The copolymer has a constitutional unit expressed as the following formula (I) and at least one of constitutional units expressed as the following formulae (II) to (IV). Methoxypolyethylene glycol methacrylate etc. are used as monomers for forming the constitutional unit of the formula (I), stearyl methacrylate etc. are used as monomers for forming the constitutional unit of the formula (II), polypropylene glycol methacrylate etc. are used as monomers for forming the constitutional unit of the formula (III), and styrene etc. are used as monomers for forming the constitutional unit of the formula (IV).