In a sitting position, many people have troubled for lumbago. As premise, lumbago was defined as rotation of a pelvis and change of a lumbar vertebra curve being the causes. So, in order to reproduce posture change on a computer and evaluate lumbago, human equivalent model was created in analyzing anatomy. The simulation result of the evaluation model was able to express mathematically changes in expansion of springs as evaluation of an ache. As a result, it was verified that the built model is appropriate to evaluate lumbago.