idx = 4;
mes = new Array(idx);

mes[0]="<a hr" + "ef='http://www.killy" + "thedolphin.com/?utm" + "_source=blogtool&utm_medium=b" + "anner&utm_t" + "erm=ktd&utm_content=ktd-vert" + "ical-b1.jpg&utm_campaign=s" + "elf' title='「イルカの" + "キリー」絶賛" + "発売中！'><img src='http://www.killythedol" + "phin.com/images/ktd-" + "vertical-b1.jpg' width='120' height='240' alt='「イル" + "カのキ" + "リー」絶賛" + "発売中！' /></a>";
mes[1]="<a href='http://www.killyth" + "edolphin.com/?ut" + "m_source=blogt" + "ool&utm_medium=b" + "anner&utm_term=ktd&utm_content=ktd" + "-vertical-b2.jpg&utm_ca" + "mpaign=self' title='「イ" + "ル" + "カのキリ" + "ー」絶賛発売" + "中！'><img src='http://www.kill" + "ythedolp" + "hin.com/images/kt" + "d-vertical-" + "b2.jpg' width='120' height='240' alt='「イ" + "ルカのキリー」絶" + "賛発売" + "中！' /></a>";
mes[2]="<a href='http://www.k" + "illythed" + "olphin.com/?utm_source=blogtool&utm_medium=banner&utm_term=ktd&utm_content=ktd-ve" + "rtical-" + "b3.jpg&utm_campaign=self' title='「イル" + "カのキ" + "リー」絶賛" + "発売" + "中！'><img src='http://www.killyt" + "h" + "edol" + "phin.com/images/k" + "td-vert" + "ical-b3.jpg' width='120' height='240' alt='「イル" + "カの" + "キリ" + "ー」絶賛発売中！' /></a>";
mes[3]="<a href='http://www.kill" + "ythe" + "dolphin.com/?utm_source=blogtool&utm_medium=banner&utm_term=ktd&utm_content=k" + "td-vertical-b4.jpg&utm_campaign=self' title='「イ" + "ルカのキ" + "リー」絶賛発売中！'><img src='http://www.kill" + "ythedol" + "phin.com/images/kt" + "d-verti" + "cal-b4.jpg' width='120' height='240' alt='「イル" + "カのキ" + "リー」絶賛発" + "売中！' /></a>";

r = Math.floor(Math.random() * idx);

document.write(mes[r]);