A marking device comprises an outer shell in a cylindrical shape with a bottom surface attached to a molding device, a rotatable tube provided inside of the outer shell, an indicator connecting to the bottom of the outer shell and a support mechanism pushing up the rotatable tube from the internal space of the outer shell while the indicator and the outer shell are engaged with each other. The head of the indicator is formed in a frusto-conical shape tapered into the inside of the outer shell. The rotatable tube comprises an inner surface contacting to the outer surface of the head of the indicator, and an outer surface forming a frusto-conical head tapered into the inside of the outer shell from a second carved marks. The outer shell comprises an inner surface contacting to the outer surface of the head of the rotatable tube.