Recently, Japan has become a nation of old people, and also shipbuilding industries are not exceptional. To increase productivity and to keep safety and health of the workers in such circumstance, the current production system must be reviewed so that it will be suitable to human oriented production. Developments of biomechanics and ergonomics, together with the computer simulation technique, help to establish a virtual ergofactory which combines productivity and humanity well. This report has picked up the welding work, which is the typical job in shipbuilding, as an example of human task simulation; the static strength prediction on human body and low back compression analysis. As a result, the torque and/or forces on segments and joints in a human body were calculated in accordance with the each working posture, and these showed that the welder would suffer from severe torque on the knee and pressure on low back at usual squat posture (flat position).