var num = 100
var ran = Math.random();
var target = parseInt(ran*num)+1;

var img1 = "top_img/catch/catch_jp1.jpg" // “Œ“ϊ–{‘εkΠver1
var img2 = "top_img/catch/catch_jp2.jpg" // “Œ“ϊ–{‘εkΠver2
var img3 = "top_img/catch/catch_jp3.jpg" // “Œ“ϊ–{‘εkΠver3
var img4 = "top_img/catch/catch_jp4.jpg" // “Œ“ϊ–{‘εkΠver4
var img5 = "top_img/catch/catch_jp5.jpg" // “Œ“ϊ–{‘εkΠver5
var img6 = "top_img/catch/catch_jp6.jpg" // “Œ“ϊ–{‘εkΠver6
var img7 = "top_img/catch/catch_jp7.jpg" // “Œ“ϊ–{‘εkΠver6
var img8 = "top_img/catch/catch_jp8.jpg" // “Œ“ϊ–{‘εkΠver6

var Link1 = "http://www.habitatjp.org/jpblog/2011/03/post-171.html" // y‹Ω‹}zu“Œ“ϊ–{‘εkΠvŽx‰‡•ε‹ΰŽσ•tŠJŽn


var URL1 = "<a href='" + Link1 + "'><img src='" + img7 + "' border='0'></a>";
var URL2 = "<a href='" + Link1 + "'><img src='" + img8 + "' border='0'></a>";
var URL3 = "<a href='" + Link1 + "'><img src='" + img6 + "' border='0'></a>";

if ((target >= 1) && (target <= 50)) { document.write(URL1) };
if ((target >= 51) && (target <= 100)) { document.write(URL2) };
if ((target >= 101) && (target <= 102)) { document.write(URL3) };