それを自分で試してみてください - JavaScript Reference onscroll3

<!DOCTYPE html>
<html>
<head>
<style>
.slideUp {
	animation-name: slideUp;
	-webkit-animation-name: slideUp;	
	animation-duration: 1s;	
	-webkit-animation-duration: 1s;
	visibility: visible;			
}

@keyframes slideUp {
    0% {
        opacity: 0;
        -webkit-transform: translateY(70%);
    } 
    100% {
        opacity: 1;
        -webkit-transform: translateY(0%);
    }	
}

@-webkit-keyframes slideUp {
    0% {
        opacity: 0;
        -webkit-transform: translateY(70%);
    } 
    100% {
        opacity: 1;
        -webkit-transform: translateY(0%);
    }
}

body {height:1500px;}
.col-1 {float:left}
.col-2 {float:left;padding-left:25px;}
img {width:180px;height:100px;visibility:hidden;}
hr {margin-top:400px;}
</style>
</head>
<body>

<p>Scroll down this page.</p>
<p>When you have scrolled 350px from the top, an image will slide in.</p>

function myFunction() {
    if (document.body.scrollTop > 350 || document.documentElement.scrollTop > 350) {
        document.getElementById("myImg").className = "slideUp";
    }
}
</script>

</body>
</html>