A load port apparatus connects a main opening of a wafer transportation container to a frame opening. The apparatus includes an installation unit, a frame unit, a flange clamp unit, and a detection unit. The installation unit includes an installation table configured to install the container and relatively move to the frame opening. The frame unit is upright upward from the installation unit and includes the frame opening. The flange clamp unit includes an engagement section and a drive section. The engagement section is engageable with a flange surrounding an outer circumference of the main opening. The drive section drives the engagement section to carry out an engagement operation and a separation operation. The detection unit detects the engagement operation by the flange clamp unit with classification into a normal engagement operation and an abnormal engagement operation.