This paper presents the efficacy of our proposed evolutionary wearable device for cervical surface body temperature measurement. For more than ten years, wearable devices that can continuously monitor/record vital signs on the wrist are widely accepted for healthcare managements. In our previous works, we have proposed wearable system mounted a cervical body surface to detect body temperature on account of him/her with non-restriction. Our wearable system is able to solve the problem that especially a physically handicapped person or an aged person who need nursing care is difficult to put the wearable devices on the wrist. This paper describes evaluation of our device performance, and then experimental verification of the efficacy of our device by long-term continuous body temperature monitoring in free-living conditions. Consequently, long-term continuous body temperature monitoring data can be obtained utilizing our device that realized the high accuracy and response.