Abstract: A parking brake apparatus comprising a manipulation lever; an actautor; a balance lever connected at its one end through a first coupling member with the manipulation lever so that a manipulated force of the manipulation lever acts on the one end and at its outer end through a second coupling member with the actuator so that an operating force of the actuator acts on the other end, the balance lever having a portion on with a parking brake force acts; relative displacement detecting unit for detecting a relative displacement between the manipulation lever and the actuator; and control means unit for controlling the actuator so that the relative displacement detected by the relative displacement detecting unit is reduced.

Abstract: In a load sensing valve including a proportioning valve (P-valve) and a deceleration sensing valve (G-valve), a compensating device is installed for varying the volume of the fluid sealing chamber of the G-valve in accordance with the magnitude of sealed hydraulic pressure in the fluid sealing chamber when the sealed hydraulic pressure is lower than a predetermined valve to change the pressure controlling characteristic of the proportioning valve.