A robot program modification device including a program storage unit that stores an operation program for a robot, a program execution unit that executes the stored operation program, a stop position estimation unit that estimates, at each operation position of the robot during execution of the operation program, a stop position of the robot in a case of cutoff of power, based on a movement speed of the robot, a stop position determination unit that determines whether the estimated stop position is in a predetermined region or not, and a speed modification unit that modifies, in a case where the stop position is determined to be outside the region, a set speed in the operation program such that a movement speed at the operation position corresponding to the stop position is reduced.