This invention concerns a rotary crane, especially an offshore crane of the king post type. The rotary crane has a pylon which can be anchored on a floor plate, platform, or similar equipment, a turntable housed to revolve around the longitudinal axis of the pylon by means of an upper support and a lower support, a crane boom supported by the turntable, and rotating gear for rotating the turntable around the pylon. The upper support has a mount which is positioned on the peak of the pylon and which can rotate, which mount has an axial support surface for axial support on the pylon as well as a radial support surface for radial support on the pylon, and suspension equipment for suspending the turntable. According to the invention, on the pylon there is an inclined plane, and there is on the mount a lifting component which can be anchored, which lifting component runs around the longitudinal axis of the pylon along the inclined plane when the mount is rotated and lifts the mount with its axial support surface off the pylon.