During overhead work, workers need to keep raising weights of approximately 2 to 4 kg with the muscular strength of their upper limbs, and the burden of this work is high. Therefore, we developed an assistive device, named TasKi, using a self-weighted compensation mechanism to reduce the burden on upper limbs during overhead work. It can compensate for upper limb weight using the force of a spring in various postures of the upper limbs, without a battery. In this study, to provide effective assistance to many users, we clarified the crucial assistance and parameter adjustment range of settings corresponding to physical differences. First, the assistive force value of TasKi to reduce the work burden of each user was confirmed via a subjective evaluation experiment and myoelectric potential measurements. Next, we conducted a test survey of TasKi users and investigated the relationship between physique and the wearing feeling. According to the survey, 80% of the subjects provided favorable opinions on the assistive method used by TasKi. Finally, we had subjects of various physiques wear the device and investigated the relationship between physique and the wearing feeling with respect to shoulder joint movements. It was observed that the subjects with greater shoulder widths experienced difficulties when moving in the direction of internal-external rotation because of the small size of TasKi. The influence on the ease of motion and perception of size was less in the direction of flexion-extension and adduction-abduction motions.

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