Edit in JSFiddle

var y;
var hinner = $(".wrapper").height();
$(".wrapper").height("300px");
var hwrapper = $(".wrapper").height();
var scroll;
var wrappertopoffset = $(".wrapper").offset().top;
$(".wrapper").on("mousemove", function( event ) {
    y =  event.pageY - wrappertopoffset; 
    scroll = (y/hwrapper)*(1-hwrapper/hinner)*(hinner);
    $(".wrapper").stop().animate({scrollTop:scroll},0);
    $("#deger").text("y : " + y + " / margin : " + $(".wrapper").offset().top + "/" + y/hwrapper + " / hinner : " + hinner + " / scroll : " + scroll);
});

<div class="wrapper">
    <div>DIV-FIRST</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV</div>
    <div>DIV-LAST</div>
</div>
<div id="deger" > </div>

.wrapper
{
    position:relative;
    margin-top:70px;
    margin-left:200px;
    background-color:brown;
    width:100px;
    overflow:hidden;
    
}
.wrapper div
{
    width:100px;
    height:50px;    
}