Abstract: The disclosed oil pressure booster includes a spool to be actuated as a brake pedal is depressed, which spool has movable parts of a throttle valve, a return path valve and a control valve, and as the spool is moved in a direction of depressing the brake pedal, the throttle valve is at first closed and then the return path valve is closed, and thereafter the control valve starts to open.

Abstract: The spool of the inching valve has first and second lands, a first portion connected to the first land and tapered or suitably formed in such a manner as to gradually increase the flow resistance of the inlet port in accordance with the axial movement of the spool into a position in which the first land fully closes the inlet port, and a second portion connected to the second land and having a reduced uniform diameter or a suitable form which initially temporarily abruptly reduces the flow resistance of the drain port and subsequently gradually reduces the flow resistance thereof in accordance with the axial movement of the spool from a position in which the second land opens the drain port.