PURPOSE: To fully eliminate the engagement and disengagement of the conventional brake lock metal fittings by providing a single operation body and a switching valve operation body and enabling the simultaneous and independent braking of a pair of hydraulic brakes by alternatively operating them.

CONSTITUTION: A two-shaft four-wheel type tractor has a pair of right and left hydraulic brakes 4R and 4L which brake a pair of right and left rear wheel shafts 3, respectively. When these hydraulic brakes are operated together, the center of an operation plate 5 is stepped on. A control valve 8 is switched through an arm 9 and a connecting lever 10 and the pressurized oil from a pump P is supplied to both hydraulic brakes 4R and 4L through a switching valve 12 which is set to the neutral position. On the other hand, for example, when the one-side shaft 3 is braked by the hydraulic brake 4R, the right side of the pedal 7 of the operation body 5 is stepped on and an operation body 14R closes. A valve body 12R is excited and the pressurized oil is supplied to only one-side hydraulic brake 4R.