The operating system for a construction machine gives advice on efficient operation to an operator. A specified state value relating to the operational condition of the construction machine, for example, the hydraulic oil pressure or engine speed, is detected (S101), and the frequency distribution of the state value in prescribed time intervals is calculated (S102). The variable range of the state value is classified into plural regions beforehand, and different target values are pre-set for each these regions. For each region, the frequency distribution is compared with the target value (S104, 106, 108, 110, 112), and as a result of the comparison, a applicable message is selected from the prescribed messages and output (S105, 107, 109, 111, 113). The output message may also be selected according to the combination of the comparison results for the plural state values such as the hydraulic oil pressure and engine speed.