In a normal state, a reaction force actuator (20) applies an operation
reaction force to an steering member (2) through a planetary gear mechanism
(6). When failure occurs in a steering actuator (12), the reaction
force actuator (20) is turned off, and a plunger (13) locks the rotation
of one element (18) which is connected to the reaction force actuator (20),
in the planetary gear mechanism (6). In turn, a manual steering mode is
set up in which a rotation of the steering member (2) is transmitted to
a pinion gear (14) at a transmission ratio of the carrier (16) holding
planetary gears (17) and a sun gear (15).
