A method and optical detection equipment for monitoring a container transfer device on lowering a container onto or lifting away from a transport platform. The container, its pin holes' position and the position of the lock pins of the transport platform are determined by the optical detection equipment, which includes a group of optical detection devices measuring obliquely from up the container and the transport platform during lowering or lifting of the container such that positions of the container and the lock pins are determined based on the measurement of the same optical detection devices.