It is desirable to design a structure and its members with a reasonable reliability. Here, a reduction factor for obtaining the design strength of a reinforced concrete member subjected to shear and flexture with a required reliability is proposed for the JSCE Code by using the probabilistic method of estimating the reliability, considering the variations in strengths of both reinforcing bars and concrete, because the reliability of the strength provided in the JSCE Code has been found to be considerably higher than that specified in all cases. The validity of the factor is examined by comparing the obtained reliability with that of the strength provided in the ACI Code which was determined on the safer side, based on a large number of test data.