To properly manage the voltage of a distribution system.

A method for managing the voltage of a distribution system 1 includes: a high-voltage distribution line 3 extended from a substation 2 for power distribution and provided with multiple nodes 4; a pole transformer 5 the primary side of which is connected to a node 4; and a low-voltage distribution line 6 connected to the secondary side of each pole transformer 5. A range of voltage drop relative to the proper voltage of the low-voltage distribution line 6 is taken as a random variable. Using this random variable, a cumulative distribution function of the ratio of customers receiving power corresponding to the range of voltage drop to all the customers receiving power from the low-voltage distribution line 6 is determined in advance. The voltage of the low-voltage distribution line 6 is quantitatively evaluated using the cumulative distribution function.