It has been thought that the physical development rate depends on the difference in potential between the silver electrode in the developer without developing agents and the redox electrode in the developer without silver-ion. Using two series of CD-3 physical developers with three levels of silver-ion activities, one series containing sodium thiosulfate, the other potassium thiocyanate as silver complexing agents, the dependence of development rate upon silver complexing agents has been invertigated by post fixationphysical development and also by tracing OH^- consumption during liquid reaction in a mixture of the physical developer and a Carey-Lea-Type colloidal silver sol. The use of thiocyanate gave faster development rate and more rounded silver grain than thiosulfate at equal silver-ion activities. Consequently, the differences in the rate of development and the form of developed silver may be due to not only silver-ion activity, but also the factors originated in the kind of silver complex.