now=new Date();

mo=now.getMonth()+1;

if (mo<2) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title01b.jpg);}--></style>')
} else if (mo<3) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title02b.jpg);}--></style>')
} else if (mo<4) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title03b.jpg);}--></style>')
} else if (mo<5) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title04b.jpg);}--></style>')
} else if (mo<6) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title05b.jpg);}--></style>')
} else if (mo<7) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title06b.jpg);}--></style>')
} else if (mo<8) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title07b.jpg);}--></style>')
} else if (mo<9) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title08b.jpg);}--></style>')
} else if (mo<10) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title09b.jpg);}--></style>')
} else if (mo<11) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title10b.jpg);}--></style>')
} else if (mo<12) {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title11b.jpg);}--></style>')
} else {
  document.write('<STYLE type="text/css"><!--#head {background-image: url(http://www.asahi-net.or.jp/~xn4m-endu/image/title12b.jpg);}--></style>')
}