Abstract: An operation panel and a monitor for displaying the operating status of the work machine and other information. The operation panel has a switch for operating a quick coupler mounted on a work arm so that the quick coupler performs attaching and detaching operation. In conjunction with operation of the switch, the monitor is switched from a default screen displaying the operating status of the work machine to a screen for prompting selection of an attachment. Connected to the monitor is a controller, to which an attachment hydraulic circuit is connected. The controller serves to switch settings for the attachment hydraulic circuit in accordance with the hydraulic attachment that has been selected by using the monitor. The invention enables reliable switching of settings for the attachment fluid pressure circuit in accordance with the attachment mounted, without requiring each attachment to be provided with identification information.