Disclosed is a hill start assist for a vehicle capable of suppressing vehicle movement contrary to driver's expectations and capable of improving driving feel even if the magnitude of detected values regarding the driving direction of driving wheels or that of driving force of the driving wheels are abnormal. Specifically disclosed is a hill start assist (1) for a vehicle comprising an ECU (20) that includes a detection state determining unit (25) that determines the detection state of a shift lever position switch (14) and a retention control unit (26) that performs retention control in which a reduction in braking force of a braking device (5) is suppressed when the operation of a brake pedal (2) is stopped. The retention control unit (26) further includes a first retention control performing unit (27) selected when determination results of the detection state determining unit (25) are normal and a second retention control performing unit (29) selected when the determination results of the detection state determining unit (25) are abnormal. The second retention control performing unit (29) performs the retention control in a manner such that the vehicle is retained in a stop state for a second stop retention time (T2) shorter than a first stop retention time (T1) set by the first retention control performing unit (27).