A liquid blow molding apparatus comprises: a mold (4) in which a preform (2) is to be placed; and a nozzle unit (6) having a supply port (9) capable of supplying a liquid from above into the preform (2) placed in the mold (4), wherein the nozzle unit (6) includes a seal body (13) that is movable among a closed position at which supply of the liquid through the supply port (9) is blocked, a first open position at which supply of the liquid through only part of the supply port (9) in a circumferential direction is allowed, and a second open position at which supply of the liquid through the whole supply port (9) in the circumferential direction is allowed.