var agent = navigator.userAgent;
        var appver = navigator.appVersion;
        var nav = navigator.appName;
        var plf = null;
        var ver = null;
        if(agent.indexOf('Mac') != -1){
                plf = "Mac";
        }else if(agent.indexOf('Win') != -1){
                plf = "Win";
        }else{
                plf = "other";
        }
        if(agent.indexOf('MSIE') == -1){
                ver = appver.charAt(0);
                if(nav == "Netscape"){
                        nav = "Netscape";
                }
        }else{
                ver = agent.charAt(agent.indexOf('MSIE') + 5);
                nav = "MSIE";
        }
        var ms = navigator.appVersion.indexOf("MSIE");
        var ie4 = (ms>0) && (parseInt(navigator.appVersion.substring(ms+5, ms+6)) >= 4);
        var winie4 = (plf == "Win") && (ms>0) && (parseInt(navigator.appVersion.substring(ms+5, ms+6)) >= 4);
        var macie5 =  (plf == "Mac") && (ms>0) && (parseInt(navigator.appVersion.substring(ms+5, ms+6)) >= 5);
        var nesc = navigator.appName.lastIndexOf("Netscape"); //一致した位置(0)を返す
        var nesc4 = (nesc >= 0) && (parseInt(navigator.appVersion.substring(0,2)) >= 4);

        var MacMozilla =  (plf == "Mac") && (nav == "Mozilla");

    if (plf == "Mac" && nav == "Netscape") {
    document.write('<LINK REL="stylesheet" TYPE="text/css" HREF="css/mac_nn.css">');
    } else if (plf == "Mac" && nav == "MSIE") {
    document.write('<LINK REL="stylesheet" TYPE="text/css" HREF="css/mac.css">');
    } else if (plf == "Win" && nav == "Netscape") {
    document.write('<LINK REL="stylesheet" TYPE="text/css" HREF="css/win_nn.css">');
    } else if (plf == "Win" && nav == "MSIE") {
    document.write('<LINK REL="stylesheet" TYPE="text/css" HREF="css/win.css">');
    }