Basic experiments were carried out concerning the possibility of continuous ice making in supercooled water in a forced flow. In the experiments, the critical conditions of ice formation and stability of supercooled water in cooled circular tubes were examined for four kinds of tube inner diameters under various Reynolds numbers. It was understood that two ice growth modes of annular ice and dendritic ice appeared in the cooling tube according to the degree of supercooling. Nondimensional correlation equations of supercooling for ice nucleation in laminar and turbulent flow regions were derived as a function of the nondimensional ratio of thermal boundary thickness to the pipe length, which length is defined as the distance from the position where the mixing average temperature of the flowing water becomes below freezing point to the pipe downstream end.