We have performed precise Hall measurements for the ferrotoroidic candidate material UNi4B. Below Néel temperature TN ∼ 20 K (corresponding to the ferrotoroidic transition temperature), a Hall voltage becomes finite even at zero field and changes proportional to the square of current density; by contrast, it is almost zero above TN. Moreover, we have found that a current-induced magnetization estimated from our Hall effect measurements is qualitatively consistent with the previous directly measured value. These results provide strong evidence for a magnetoelectric phenomenon uniquely in ferrotoroidic metals-a zero-field nonlinear Hall effect resulting from the current-induced magnetization connecting the ferrotoroidal moments.