An inflatable swim fin apparatus includes a foot portion having a lower wall with a peripheral edge and having an upper wall extending upwardly from the peripheral edge of the lower wall, the lower wall and the upper wall defining a foot pocket and a rear opening allowing a user’s foot to be received into the foot pocket. In a non-volatile semiconductor memory device, when a selected memory cell transistor is caused to accumulate electric charges, high voltage as writing prevention voltage is applied from a PMOS transistor while low voltage as writing voltage is applied from an NMOS transistor. The coercivity Hc2 of the second ferromagnetic layer is larger than that Hc1 of the first ferromagnetic layer. Such a structure can enhance bending rigidity and twisting rigidity relative to the key-arranged direction. When multiple successive frames are determined as having invalid backgrounds, the camera represents an invalid camera. Each flocculent handling assembly includes a submerged beach and a scraper assembly including a scraper blade which extends upwardly from the beach.