In a photographic processing apparatus for immersing and developing an exposed light sensitive material in a developer contained in a developing tank, the temperature of the developer is detected and an evaporation amount of the developer corresponding to an elapsed time period is estimated on the basis of the temperature detected. Then, a replenishment water is supplied to the developing tank by the amount based on this estimated evaporation amount. Consequently, an optimum concentration of the developer in the developing tank can be maintained, thereby preventing a change in the developing characteristics.