The gravitational-wave (GW) detectors LIGO and Virgo sent out 56 GW alerts during the third observing run (O3). The Japanese Collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical and near-infrared observations to identify an electromagnetic (EM) counterpart. To facilitate follow-up observations, we have developed a web-based system to share information on candidate host galaxies and the status of the observations. Candidate host galaxies are selected from the GLADE catalog with a weight of 3D GW localization map. Using these systems, we performed galaxy-targeted and wide-field blind surveys, real-time data analysis, and visual inspection of transient candidates. We conducted galaxy-targeted follow-up observations of 23 GW events during O3. We successfully started observations for 10 GW events within 0.5 days after the GW detection. This result demonstrates that our follow-up observation has the potential to constrain EM radiation models for a merger of binary neutron stars at a distance of up to $\sim$100 Mpc with a probability area of $<$ 500 deg$^{2}$. We have also performed the follow-up for the fourth observing run (O4).