Sen:

Is that a bolt, or a nut that you see at the end of the wiper arm? If it's a nut, simply make sure the wiper arm is horizontal, and tighten it. Don't overdo it though, since the end of the wiper arm is made of a soft alloy material (maybe someone else knows what this stuff is) that is pressed onto a spline extending from the wiper linkage.

This is a fairly common problem, with a simple fix.