text-align: center для родительского блока:
<!DOCTYPE html>
<title></title>
<style>
html{width:1200px;}
.work-box-news {
background:#F0F0F0;
min-height:800px;
border-bottom: 1px solid #C1C1C1;
border-top: 1px solid white;
border:3px solid gold;
text-align: center;
}
.work-box_center-news {
width: 940px;
min-height:800px;
padding:20px 0;
position:relative;
display:inline-block;
vertical-align:auto;
border:3px solid black;
}
.left-area-work{
border:1px solid #929292;
background: #FAFAFA;
width: 240px;
min-height: 723px;
float:left;
border:3px solid green;
}
.include-work_area{
position: relative;
width: 650px;
min-height: 500px;
font-family: PT Sans;
left:25px;
float:left;
border:3px solid red;
}
</style>
<div class="work-box-news">
<div class="work-box_center-news">
<div class="left-area-work"></div>
<div class="include-work_area"></div>
</div>
</div>