We know that constituent quark model works very well to describe mesons and baryons. However, we do not know “why” it works so well. In order to understand the nature of the constituent quark, the B-factory experiment is a powerful probe. Belle is an asymmetric energy e+e- collider experiment constructed to study the CP-violation in the B-meson decay to prove the Kobayashi-Maskawa theory. Unexpected bonus of the Belle is discoveries of a large number of “new hadrons” which include candidates of exotic states such as X(3872). In this talk, an overview the hadron spectroscopy at Belle and report some details on the recent studies on exotic charmonium and charmed baryons are presented. Finally, the prospect of hadron spectroscopy at the upcoming Belle II experiment is presented.