In a workflow execution system, work control information for executing a work assigned to one of a plurality of image processing apparatuses connected to a network; workflow execution information indicating which works of a workflow have been executed; and information indicating an image processing apparatus on the next tier, are stored in a portable recording medium. When the work is executed by a proxy image processing apparatus, it is judged from the information stored in the portable recording medium whether or not the work can be executed by the proxy image processing apparatus, and if it can be executed, the work is executed based on the information stored in the portable recording medium. When proxy execution of the work is completed, workflow execution information including the execution result and image information are stored in the portable recording medium and transmitted to the image processing apparatus on the next tier.