In this study, we propose an improved active disturbance rejection control (ADRC). The basic idea behind ADRC is to model a system with a disturbance that represents any difference between the model and the actual system, including external disturbances. In the proposed method, the state-feedback gain, the integral gain, and the observer gain are determined with the pole placement method using Ackermann's formula. The effectiveness of the proposed method was confirmed using the simulation results.