Registration page problem.

I made a new registration page, but I get this error:
Fatal error: Call to undefined function: filter_var() in c:\appserv\www\reg.php on line 175

This is line 175:
if(!filter_var($email, FILTER_VALIDATE_EMAIL)){$error[]= "E-mail is not valid";}

there is missing fucntion called filter var
if you're using class u must use $this->filtervar
or if you're coding outside the class use $classname->filtervar

or if you ain't using classes at all i suggest you to make sure that you've included the page that have the function