Weak values in a pre- and post-selected system are typically measured by weak measurement, in which a probe system is weakly interacted with the systems to be measured. In weak measurement, however, the need for preparing an additional degree of freedom as the probe system complicates the measurement system. In this study, we propose a direct measurement method of weak values without using probes while maintaining the condition that the pre- and post-selected systems are hardly disturbed. In this method, a small transformation is given to the pre- and post-selected systems, and the weak value of the derivative of the small transformation is obtained from the change of the post-selection probability amplitude. This method can be applied to basically all the experiments measuring weak values instead of weak measurement and can simplify the weak value measurement systems.