The stress evaluation is of importance 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). The HRV is usually obtained from R-R intervals in an electrocardiogram (ECG). However, the use of the electrocardiogram is not suitable for a long time monitor, since several electrodes have to be directly attached to a human body in order to acquire the ECG data. We report here on a new evaluation method of the stress using a microwave reflectometer which has the features of non-contact and noninvasive method.