[Nagoyankee]

ならざる　is an old way of saying ならない、ではない、でない、etc. This form is still used by the better speakers and writers of our country today.

なる here pretty much means 'to be', and ざる serves to negate it. 人間ならざる者, therefore, means 'one that isn't human'.

The phrases most often heard using ざる would be:

帰らざる日々

思わざるできごと

～～と言わざるを得ない