Abstract: The present invention provides a container door lock pin which includes a bolt and a nut, which can lock a container door by simply pushing the bolt into the nut without needing to screw it in, and which makes it possible to visually confirm locking. The bolt has a head at its rear end and a shank. The shank has an annular groove formed in its periphery at the first position spaced from the bolt front end by a first distance. A ring spring is fitted in the groove. The nut has a bore for slidable engagement with the shank. The bore has a first annular groove formed near the nut front end. An elastic rigid confirmation seal plate is fitted in the first groove. The bore includes a cylindrical portion, which extends between the first groove and the second position spaced rearward from the first groove by a second distance, and a conical portion, which extends between the second position and the nut rear end.