The present invention provides a crane where a spreader retainer is disposed on a rear surface of an extreme end of the lowest boom portion used both for a tower boom and a normal boom, a distance between an upper spreader, which constitutes a boom raising/lowering apparatus, and a lower spreader at the maximum boom raise angle and the length of the lowest boom portion are set such that the upper spreader can be lowered to the position of the spreader retainer if the boom raising/lowering apparatus lays the boom on the ground, and a boom raising/lowering rope is then loosened for disassembly of either the tower or normal boom. Consequently, the upper spreader can be lowered to the position of the spreader retainer on the lowest boom portion when the boom is disassembled either for the tower crane or normal crane specification.