A lock apparatus of a seat for a vehicle includes a striker, a base including a first groove portion, a hook including a second groove portion and pivoting between a lock position and an unlock position, a pawl restraining a pivotal movement of the hook towards the unlock position while allowing the pivotal movement of the hook towards the lock position, a cam member including a cam profile for allowing the pivotal movement of the hook towards the lock position and for restraining the pivotal movement of the hook towards the unlock position, and a first biasing member. When the hook is pivoted to the lock position, the striker is positioned between the rotational shaft of the hook and the rotational shaft of the pawl, and the pawl and the hook are engaged at an opposite position of the rotational shaft of the hook relative to the striker.