A hydraulic control apparatus for an automatic transmission including two
frictional coupling devices of a first group and a plurality of
frictional coupling devices of a second group, the control device
including a second-group-engaging switching valve arranged to receive
second engaging hydraulic pressures generated to engage the coupling
devices of the second group and operable, upon reception of at least one
of the second engaging hydraulic pressures, to generate a
second-group-engaging pilot hydraulic pressure, and a fail-safe valve to
receive at least one of first engaging hydraulic pressures generated to
engage the two coupling devices of the first group and operable, upon
simultaneous reception of the first engaging hydraulic pressure generated
to engage one of the two coupling devices of the first group and the
second-group-engaging pilot hydraulic pressure, to prevent application of
the first engaging hydraulic pressure to the other of the two coupling
devices of the first group.