PURPOSE: To enable the combination, storage and replacement of construction work machine device to be conducted at need so as to accelerate the mechanization of construction work. CONSTITUTION: The position space of one or plural independent working devices A1, A2 traveling on expansion arms 9 in working machines W1, W2 expandable and rotatable in the horizontal direction is set so as to perform required work independently or in cooperation. In the case of performing different types of work, the arm 9 is placed to face a specific storage rack out of storage racks 57 installed on the same plane as the working devices, and the spent working device is let travel into this empty storage rack 57 for storage. Another following working device is received from the storage rack 57 so as to be mounted onto the arm 9 and moved into a required place to perform required work. COPYRIGHT: (C)1993,JPO&Japio