A control algorithm constructing device that constructs a control algorithm controlling the motion of a robot, and a controller that controls the motion of the robot in accordance with the constructed control algorithm, with the purpose of reducing the cost and time taken to create the control algorithm as compared with the conventional method such as an MZP method to solve a mechanical equation, in which the control algorithm is constructed by a recurrent neural network (RNN) including a neuron generating an output with an analogue lag with respect to an input, the coefficients of the RNN are determined in succession from the term of lower degree to the term of higher degree.