The molecular generation method developed in this study is a molecular graph-based optimization method for a given arbitrary molecule based on an evaluation function. The method performs a tree search with the molecule to be optimized as the root, by adding and deleting fragments based on the upper confidence bound (UCB) score. Fragments to be added are generated atom by atom with MCTS, and the efficiency is enhanced using a GCN model. Generating fragments atom by atom allows the molecule to be further optimized locally (only partial conformational changes).