A pod opener for opening a container, the container storing cassettes supporting substrates stacked vertically at a predetermined position, and configured to allow the substrates supported by the cassettes to be accessible by a substrate holding member of a transportation device (6, 72), comprising: an elevating mechanism elevating the stacked cassettes in a vertical direction; characterized in further comprising: a first hook member configured to engage with an engagement means of a certain first cassette among the stacked cassettes and supporting the first cassette; a second hook member configured to engage with an engagement means of a second cassette disposed immediately below the first cassette supported by the first hook member and supporting the second cassette; a forward and backward movement mechanism configured to move the first hook member and the second hook member forward so as to be closer to the cassettes when engaging with the engagement means of the first and second cassettes and moving the first hook member and the second hook member backward so as to be away from the first and second cassettes when releasing the engagement from the engagement means of the first and second cassettes; an urging member configured to urge the second hook member upward; and an atmosphere maintaining device configured to maintain an internal space having the cassette disposed therein in a predetermined atmosphere, wherein the second hook member is configured to be displaced upward by an urging force of the urging member when the second cassette is not supported and is configured to be displaced downward by a weight of the second cassette against the urging force of the urging member when the second cassette is supported. an elevating mechanism elevating the stacked cassettes in a vertical direction; characterized in further comprising: a first hook member configured to engage with an engagement means of a certain first cassette among the stacked cassettes and supporting the first cassette; a second hook member configured to engage with an engagement means of a second cassette disposed immediately below the first cassette supported by the first hook member and supporting the second cassette; a forward and backward movement mechanism configured to move the first hook member and the second hook member forward so as to be closer to the cassettes when engaging with the engagement means of the first and second cassettes and moving the first hook member and the second hook member backward so as to be away from the first and second cassettes when releasing the engagement from the engagement means of the first and second cassettes; an urging member configured to urge the second hook member upward; and an atmosphere maintaining device configured to maintain an internal space having the cassette disposed therein in a predetermined atmosphere, wherein the second hook member is configured to be displaced upward by an urging force of the urging member when the second cassette is not supported and is configured to be displaced downward by a weight of the second cassette against the urging force of the urging member when the second cassette is supported. a first hook member configured to engage with an engagement means of a certain first cassette among the stacked cassettes and supporting the first cassette; a second hook member configured to engage with an engagement means of a second cassette disposed immediately below the first cassette supported by the first hook member and supporting the second cassette; a forward and backward movement mechanism configured to move the first hook member and the second hook member forward so as to be closer to the cassettes when engaging with the engagement means of the first and second cassettes and moving the first hook member and the second hook member backward so as to be away from the first and second cassettes when releasing the engagement from the engagement means of the first and second cassettes; an urging member configured to urge the second hook member upward; and an atmosphere maintaining device configured to maintain an internal space having the cassette disposed therein in a predetermined atmosphere, wherein the second hook member is configured to be displaced upward by an urging force of the urging member when the second cassette is not supported and is configured to be displaced downward by a weight of the second cassette against the urging force of the urging member when the second cassette is supported.