The stress evaluation becomes important for the prior prevention of stress-related illnesses. One of the methods is to analyze the fluctuations of heartbeat called by heart rate variability (HRV), since the heartbeat interval is constantly fluctuating by reflecting autonomous nerve activity. The HRV has been obtained from peak intervals in an electrocardiogram (ECG). However, the use of the ECG is not suitable for a long time monitor, since several electrodes have to be attached to a human body. We report here on an evaluation method of the heart rate variability and stress using a microwave reflectometer with frequency of 10 GHz. The key technical developments (phase detector with AGC amplifier, data processing for HRV evaluation) are described. The protocol for stress evaluation examination is prepared in order to apply to various testee. The values of HRV and its spectra obtained by a reflectometer are in good agreement with those obtained by ECG.