The present paper aims to investigate two characteristics; task performance and muscular load during skill process for the pen-tablet input system with the mouse input system on the PC in order to determine the comprehensive usability for the pen-tablet system. Two computer tasks were designed for the study: task SL and task PT. Task SL was a repetitive computer-drawing including typical mouse motions such as clicking and drag-dropping. Task PT was a polgon tracing task requiring fine-controlled movements with the input device. Surface electromyography (EMG) and performance data were measured during the task. When the pen-tablet was being used, low amplitudes of EMGs for the biceps brachii, the flexor digitorum superficialis, and the extensor digitorum were found, whereas no EMG difference for the trapezius was found for both tasks. On the first day, the performance with the mouse was much higher than the performance with the pen-tablet in terms of error rates and the number of completed trials. However, the performance with the pen-tablet exceeded the performance with the mouse from the second day on, and the subjects performed better with the pen-tablet than with the mouse. Current results imply that the skill process for the pen-tablet system was very short and the subjects felt comfortable to use the new system from the beginning.