A robot controller controls an arc motion of a robot. The robot controller includes an interpolation point setting unit that sets an interpolation point between movement points in an operation program. The robot controller includes a movement-point angle calculation unit that calculates an angle relating to a reference direction for determining the orientation of the robot, and an interpolation-point angle calculation unit that calculates an angle relating to the reference direction at an interpolation point by interpolating angles relating to the reference direction at the movement points. The reference direction is a direction independent from the positions of the movement points and is set in an operation program in a predetermined coordinate system.