An exhaust gas purification system of a working machine is operable to reduce a loss of a working time caused by a point that it takes a long time to renew an exhaust gas purification device by throttle devices. The exhaust gas purification system of the working machine is provided with a common rail type engine which is mounted to the working machine, an exhaust gas purification device which is arranged in an exhaust system of the engine, and at least one of the intake air throttle device and the exhaust gas throttle device. It is provided with mode selection input means which selects whether an auxiliary renewing mode is executed or a forced renewing mode is executed in the case that a clogged state of the exhaust gas purification device is equal to or more than a prescribed level.