the reverse stall valve 33 there extends an output pressure passage 36 a spool of the reverse stall valve 33 is biased in a direction by a spring 37 and the pressure u201c po u201d in the output pressure passage 36 is applied to the spool in a direction against the spring 37 the low and reverse pressure passage 14 extends from the reverse stall valve 33 to the low and reverse brake u201c l amp r b u201d the reverse stall valve 33 is so constructed and arranged as to carry out the following operation that is when the output pressure u201c po u201d from the low and reverse amp valve 32 is under a predetermined switching pressure u201c pco u201d the valve 33 takes a first position to feed the output pressure u201c po u201d of the valve 32 to the low and reverse brake u201c l amp r b u201d while when the output pressure u201c po u201d from the valve 32 exceeds the predetermined switching pressure u201c pco u201d the valve 33 switches to take a second position to feed the line pressure u201c pl u201d to the low and reverse brake u201c l amp r b u201d in addition to the above the low and reverse amp valve 32 is constructed and arranged to have a gain viz the rate of change of the output pressure u201c po u201d of the valve 32 to change of the solenoid pressure.