A wheeled working machine having a travel base provided with front wheels and rear wheels, a main body mounted on the travel base, a working equipment attached to the main body, and a hydraulic drive system being provided with a travel motor for driving the travel base, a traveling directional control valve for controlling the travel motor, a travel control device for switchingly operating the traveling directional control valve, a brake system for braking the front wheels and rear wheels, a braking directional control valve for controlling the brake system, a brake control device for switchingly operating the braking directional control valve, characterised in that the hydraulic drive system further comprises a brake control amount sensor for detecting a control amount of the brake control device, a selector switch capable of selecting a work brake mode which is a temporary stop mode for the travel base to be performed upon conducting work by the working equipment, a proportional solenoid valve capable of controlling the braking directional control valve, a controller capable of outputting a brake actuation signal or brake release signal to the proportional solenoid valve responsive to a signal outputted from the brake control amount sensor, and a travel control amount sensor for detecting a control amount of the travel control device, wherein the controller further comprises a delay means for introducing a time delay into the brake release signal responsive to a signal outputted from the travel control amount sensor and is adapted to perform processing such that the brake release signal as delayed by the delay means is outputted to the proportional solenoid valve, wherein the delay means comprises a low-pass filter for passing the brake release signal and a coefficient setting unit for setting a coefficient corresponding to a control amount outputted from the travel control amount sensor, and wherein the controller is adapted to perform processing such that pass characteristics for the brake release signal through the low-pass filter are controlled to pass characteristics corresponding to the coefficient set by the coefficient setting unit. a travel motor for driving the travel base, a traveling directional control valve for controlling the travel motor, a travel control device for switchingly operating the traveling directional control valve, a brake system for braking the front wheels and rear wheels, a braking directional control valve for controlling the brake system, a brake control device for switchingly operating the braking directional control valve, characterised in that the hydraulic drive system further comprises a brake control amount sensor for detecting a control amount of the brake control device, a selector switch capable of selecting a work brake mode which is a temporary stop mode for the travel base to be performed upon conducting work by the working equipment, a proportional solenoid valve capable of controlling the braking directional control valve, a controller capable of outputting a brake actuation signal or brake release signal to the proportional solenoid valve responsive to a signal outputted from the brake control amount sensor, and a travel control amount sensor for detecting a control amount of the travel control device, wherein the controller further comprises a delay means for introducing a time delay into the brake release signal responsive to a signal outputted from the travel control amount sensor and is adapted to perform processing such that the brake release signal as delayed by the delay means is outputted to the proportional solenoid valve, wherein the delay means comprises a low-pass filter for passing the brake release signal and a coefficient setting unit for setting a coefficient corresponding to a control amount outputted from the travel control amount sensor, and wherein the controller is adapted to perform processing such that pass characteristics for the brake release signal through the low-pass filter are controlled to pass characteristics corresponding to the coefficient set by the coefficient setting unit.