Edit in JSFiddle

$('#submit').attr("disabled","disabled"); 
$('#check').click(function(){
     
    if($(this).prop('checked') === false){
         $('#submit').attr("disabled","disabled");   
    }
    else {
        $('#submit').removeAttr('disabled');
    }
});

div{margin:50px;}

<div><input type="checkbox" id="check"><a href="javascript:void(0);">利用規約</a>に同意して送信する
    <input type="submit" id="submit" value="submit"></div>