function external_link(){
   var host_Name = location.hostname+'';
   var host_Check;
   var link_Href;

	host_Name = host_Name.replace(new RegExp('^www.'), '');
	var reg = new RegExp('^(www.|)'+host_Name);

   for(var i=0; i < document.links.length; ++i)
   {
       link_Href = document.links[i].host;
       host_Check = link_Href.indexOf(host_Name,0);
		
		if( link_Href.match(reg) ){
			//do nothing
		}
		else{
			document.links[i].target="_blank";
		}
   }
}
window.onload = external_link;