To make an operation tool of the special specification exhibit operability almost equivalent to that of an operation tool of the standard specification even if a work attachment of a working machine is replaced from that of the standard specification to that of the special specification.

A hydraulic shovel 1 is configured to make the replacement of a work attachment 4 from that of the standard specification to that of the special specification. When correcting a flow rate to each cylinder 8, 9, and 10 according to each replaced work attachment, the flow-rate correction is executed as follows. The work attachment is set in first/second postures so as to calculate the maximum moment around the axial center of each work attachment of the special specification. Each calculated maximum moment and each maximum moment of the work attachment of the standard specification are compared with each other so as to set the correction opening amount of a flow control valve on the basis of the comparison. The flow-rate correction of each flow control valve is executed on the basis of the set correction opening amount.