The property of the light-developable printing-out emulsion co-precipitated with metallic ion is described. The tested metallic ions are classified into four types, according to the effect on the printingout characteristics; the accelerating type which relatively increases the image density D_a more than the background density D_b , the reversal type which increases more D_b than D_a , the parallel type which increases or decreases simultaneously both D_a and D_b , and the last the ineffective type. Those of the accelerating type are useful as “ visibilizer ” for the latent image of the lightdevelopable printing-out emulsion. The metallic ions belonging to the accelerating and reversal type have specific effects on printing-out and developing-out characteristics of AgX emulsion. The behaviours of Pb²⁺, Au³⁺ and Bi³⁺ representing of them have been observed.