We discuss whether the Stern-Gerlach experiment accepts hidden-variables theories. We discuss that the existence of two spin-1/2 pure states $|\uparrow\rangle$ and $|\downarrow\rangle$ rules out the existence of probability space of specific quantum measurement. If we detect $|\uparrow\rangle$, then measurement outcome is $+1$. If we detect $|\downarrow\rangle$, then measurement outcome is $-1$. This hidden-variables theory does not accept the transition probability $|\langle\uparrow|\downarrow\rangle|^2=0$. Therefore we have to give up the hidden-variables theory. This implies the Stern-Gerlach experiment cannot accept the specific hidden-variables theory. And we study whether quantum phase factor accepts hidden-variables theories. We use the transition probability for two spin-1/2 pure states $(|\uparrow\rangle+|\downarrow\rangle)/\sqrt{2}$ and $(|\uparrow\rangle+e^{i \theta}|\downarrow\rangle)/\sqrt{2}$. It is $\cos^2(\theta/2)$. We discuss that the phase factor does not accept another specific hidden-variables theory. We explore the phase factor is indeed a quantum effect, not classical. Our research gives a new insight to the quantum information processing which relies on quantum phase factor, such as Deutsch's algorithm.