We succeeded in on-chip platelet production using a bioreactor with a curve-shaped 3D microchannel. In order to produce platelets from megakaryocytes (MKs) in a microfluidic chip, it is required to trap MKs and to apply fluid force to it. Since MKs have a relatively big distribution in their size, it is difficult to effectively trap MKs by using conventional microfluidic chips having uniformly patterned pillars with discrete pitch size. Thus, we proposed a curve-shaped 3D microchannel whose height gradually decreases along the flow pass to trap MKs of various size. We fabricated the curve-shaped 3D microchannel by using grey-scale lithography and deep reactive ion etching (DRIE) techniques. Since our microfluidic chip was packaged by a glass substrate, we can observe the processes of platelet production with a time-resolved technique. Through the experiments of on-chip platelet production using MKs induced from human induced pluripotent stem cells (hiPSCs), we successfully trapped the MKs of various size corresponding to the channel height. The trapped MKs were exposed to fluid force in the microchannel, and resulted in producing platelets.