The　purpose　of　this　article　is　to　propose　introducing　a　marketing　concept　to　Japanesepublic　libraries　for　adapting　to　the　outside　environment．　ln　the　first　part，　marketing　concept　inpublic　libraries　is　defined　as　a　key　concept　to　build　a　long－term　relation　with　various　stakeholders　including　customers　and　improve　the　effect　on　the　whole　society．　Secondly，　“publicresponsibility　of　libraries”　is　summarised　as　the　basis　of　marketing　in　public　libraries．　One　is　tocorrect　market　failure　from　the　viewpoint　of　economics，　and　the　other　is　to　contribute　to　theformation　of　public　knowledge　from　the　viewpoint　of　sociology．　ln　the　third　part，　the　authoradvocates　nich　strategy　as　the　optimal　solution　to　such　social　expectation．　Furthermore，　theframework　of　competitive　analysis　aiming　to　understand　the　outside　environment　is　suggested．