According to a container coupling device 1 of an embodiment, when a container has been lifted with an upper fitting (4) and a lower fitting (5) being engaged with corner fittings (F) of an upper container and a lower container, respectively, via a spring mechanism, a container weight acts on a lower half portion (42) of the upper fitting (4) that crosses an engaging hole (Fa) of the corner fitting (F) of the upper container and on an upper half portion (51) of the lower fitting (5) that crosses an engaging hole (Fa) of the corner fitting (F) of the lower container. The upper fitting (4) and the lower fitting (5) are forcibly rotated against a biasing force of the spring mechanism in a direction in which the upper fitting and the lower fitting overlap an upper fitted portion (22) and a lower fitted portion (23), respectively. As a result, the lower fitting (5) rotates to a position at which the lower fitting overlaps the lower fitted portion (23) while the upper fitting (4) is engaged with the bottom corner fitting (F) of the upper container, and is thus released from the corner fitting (F).