In order to develop a non-invasive and non-contact vital sign monitoring system during sleep, we use a commercially-available depth sensor, Kinect for Windows v2, to obtain subject's respiratory data without any contact to his/her body. In the experiment, the depth sensor points at either chest or abdomen while a subject lies on a bed. The results are evaluated in terms of installation position of the depth sensor, and compared with the data from conventional contact-type respiration sensor. Experimental results reveal that the respiration frequency obtained from the depth sensor matches to the one from the contact-type respiration sensor when the subject lies on his/her back with one's head turned to upward. Moreover, the abdomen gives a larger signal than the chest. When the body is captured at the peripheral region of the sensing sight, however, the s/n ratio becomes lower. The higher the installation position is, the more artifact the system has.