The occurrence ratio of intracloud (IC) to cloud-to-ground (CG) discharges, which is denoted by -ratio, is the crucial parameter for the studies on the climatological differences of thunderstorm structures and the quantitative evaluation of lightning contributions to the global electric circuit. However, the latitudinal, regional, and seasonal dependences of -ratio are not fully clarified. Therefore, using optical data obtained by the JEM-GLIMS mission, we distinguished the lightning discharge type, , IC, positive CG (+CG), and negative CG (-CG) discharges, and statistically estimated the Z-ratio. We analyzed 8354 JEM-GLIMS lightning events and succeeded in identifying 4431 IC discharges, 597 +CG discharges, and 3326 -CG discharges. From this result, we calculated the -ratio and estimated its latitudinal, regional, and seasonal dependences. It is found that the -ratio is slightly higher over the continental area than the oceanic area. In addition, the average -ratio in the local summer season is higher than that in the local winter season. The clear latitudinal dependence of the -ratio is also found, which is generally comparable to the results shown in the previous studies. The estimated -ratio varies from 2.9 - 0.19 from the equator to 50º latitude, and the global mean value is 1.6. The regional dependence of -ratio derived from this study can be combined with the CG lightning data provided by the ground-based lightning detection networks to estimate the occurrence number of IC discharges. It will greatly contribute to a more accurate estimation of the total lightning currents in the global electric circuit.