Tooth flank form deviation of micrometers influences vibration and noise characteristics of gears and therefore strict quality control of tooth flank form is demanded. However, since gear checker is structurally-complex, it is difficult to analyze how error factors of gear checkers influence the measurement result. In this research, Virtual Gear Checker (VGC) is proposed, which is a simulation program of gear measurement considering the mechanisms and motions of gear checkers and possible error factors. The influence of the error factors on the measurement result can be clarified by VGC. VGC is also able to calculate the theoretical measurement result of non-involute helicoid artifact. It is easy for VGC to measure tooth flank form repeatedly in virtual space and therefore it can assess the uncertainty of measurement with gear checker. The uncertainty of gear measurement is calculated as an example.