A task management server includes a memory unit for memorizing task information containing constituents indicated by a task property of a supported task, an action entry comprising a task, an event rule and a main task and subtask structure, and each of a plurality of client machines includes a task information display/operation unit which enables each user to operate information during a task is executed. A task execution support system supports the user such that the user can execute a task while determining the contents of action and the procedure of action in accordance with a progress of a task without defining a series of action procedure from the start to end of a task with all sorts of actions in the task listed-up as a network type flow before a task to be supported is started.