To provide a vehicular seat unlocking device reliably retracting a seat in a head-on collision of a vehicle, and preventing the retraction of the seat in a rear-end collision.

The vehicular seat unlocking device comprises: a pair of lower rails 16a, 16b extending in the advancing direction and arranged on a floor 11a; a moving member 14 mounted on the pair of lower rails; a pair of upper rails 17a fixed to a seat 13 and mounted on a movable member or the pair of lower rails; a seat fixing means 20 to fix the upper rails; a pair of locked members 31 provided on the lower rails, respectively; a housing 32 provided on the movable member; a pair of locking tools 33 protruded sideways from the housing 32; a sliding piece 35 movably stored in the housing 32; a driving means 41 to move the sliding piece; a load sensor 42 to detect the load on the seat 13; and a controller 43 to control the driving means 41 based on the detected output of the load sensor 42.