var banner = new Array();

banner[0]='https://i.servimg.com/u/f33/15/43/42/30/banpan11.png';
banner[1]='https://i.servimg.com/u/f33/15/43/42/30/bansha10.png';

document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];