A telescopic boom provided in a crane includes a boom body and a telescopic cylinder for extending/contracting the boom body. A roller is provided in a tip end portion of the telescopic cylinder to be rotatable in a longitudinal direction. A peripheral surface of the roller is formed to be curved (crowning) in a convex shape outside as viewed in the longitudinal direction and make contact with a lower plate of the boom body in a state where both corner parts are away from the lower plate.