Patent ID: 7641282

Claim:
A locking device for a seat back, comprising: a lock plate fixed to a vehicle body and having one or more lock holes; a base plate fixed to a seat back; a lock pin freely slidably supported on the base plate and urged by first urging means, the lock pin entering into one of the lock holes of the lock plate at a predetermined rising angle, thereby holding the seat back at the predetermined rising angle; a lift lever having a first arm portion and a second arm portion and pivotally attached onto the base plate, the lift lever being urged to an initial position by second urging means; and a guide hole formed in the lock plate, the guide hole allowing the second arm portion of the lift lever to enter thereinto when the seat back is held at a rising position, in which, when the seat back is rotated to rise, the second arm portion is lifted up by a front end edge of the guide hole, and rotates positively from the initial position, and then enters into the guide hole while rotating reversely, whereby the first arm portion pushes up the lock pin to thereby avoid the lock pin colliding with the lock plate, and thereafter, the first arm portion permits the lock pin to enter into the lock hole, wherein, on the base plate, there is provided a step difference portion that prevents the lift lever from rotating positively by a fact that the second arm portion of the lift lever abuts on a side edge portion of the guide hole of the lock plate when the base plate rotates forward about the lock pin along a horizontal direction in an occasion where a load is applied to the seat back from a rear direction when the seat back is held at the rising position.