Expansion device and crane

An expansion device that expands and contracts an expandable boom having a first boom element and a second boom element which expandably overlap each other, the expansion device comprising:

• a first hydraulic source that discharges a first working fluid;
• an expandable cylinder that has a fixed part and a movable part movable with respect to the fixed part, is operated based on supply of the first working fluid, and moves the first boom element with respect to the second boom element in a stretching direction;
• a second hydraulic source that is provided in the movable part, discharges a second working fluid, is a hydraulic source different from the first hydraulic source, and has a tank, an electric motor, and a hydraulic pump driven by the electric motor;
• a first connecting mechanism that is provided in the movable part, is operated based on supply of the second working fluid, and switches between a connected state and a disconnected state between the first boom element and the movable part;
• and
• a second connecting mechanism that is provided in the movable part, is operated based on the supply of the second working fluid, and switches between a connected state and a disconnected state between the first boom element and the second boom element.