We have been developing a grip aid system using air cylinders to assist elderly who have weak grasping force to have daily living activities. The system is small and light weight. In this paper, mechanism to assist thumb, index, and middle fingers using one air cylinder for each finger, is proposed. And also control method of the device using a bending sensor to transfer their will to control the system is developed. Finally much kind of objects are grasped with an assist of the system and the result shows a potential of the system.