A blow molding device includes: a tubular-shaped nozzle; a tubular-shaped sealing body configured to be displaced between closing and opening positions; and a stretching rod surrounded by the sealing body. The sealing body includes a tubular wall, which has a drawing-in hole extending from one end to another end, the one end being open at a lower end of the tubular wall, and the other end being open at an outer circumferential surface of the tubular wall. The nozzle has a drawing-in path configured to communicate with the other end of the drawing-in hole when the sealing body is in the closing position. The blow molding device further includes a fluid drawing-in source configured to draw in the incompressive fluid from the drawing-in path.