To face the decrease of lifestyle comfort, the augmentation of hypothermia risks, and the deterioration of labor productivity resulting from energy consumption reduction policies, we have been proposing a wearable air-conditioning device worn like a scarf. This paper reports evaluation results of this wearable air-conditioning device’s effectiveness regarding comfort in hot summer office environment. We studied through trial subjects how neck cooling affects (1) subjective evaluation on comfort, thermic, and sweat sensations, and (2) human physiology when performing various deskwork tasks in summer heat environment. The environment of a typical Japanese office space in summer heat were reproduced using an environment control room. The environment control room’s temperature, humidity and wind velocity were set to re-create summer heat office environment (32°C, 60%, 0.15 m/s). 16 healthy subjects sat in the room in both normal condition and neck cooling condition. All subjects were dressed respecting the standard “cool-biz” dress code in Japan. (1) Comfort sensation, thermic sensation, and sweat sensation were evaluated by self-assessment. For all subjects, both discomfort sensation, heat sensation, and humidity sensation increased together with room temperature elevation, such we can understand that there is a clear correlation between environment temperature and comfort regarding temperature sensation. (2) Furthermore, we could quantitatively define the correlation between self-assessment, temperature variations, and physiological signals such as sweat amount and heart rate variability, by investigating the individual differences for comfort/discomfort in both normal and neck cooling conditions. Experimental results of this study show that using the wearable air-conditioning device in summer heat office, air-conditioner can be turned off or temperature set higher, without affecting comfort.