A seat structure including a seat cushion having a cushioning member for a seat cushion stretched across a cushion frame, and a seat back having a cushioning member for a seat back stretched across a back frame, comprising: a supporting pressure adjusting means for the seat cushion for changing a supporting pressure of the cushioning member for the seat cushion, wherein the supporting pressure adjusting means for the seat cushion comprises: a cloth spring provided on the back of the cushioning member for the seat cushion and stretched across the cushion frame; and a cloth spring adjusting member to adjust tension of the cloth spring, wherein said cloth spring adjusting member adjusts the tension of the cloth spring to change the supporting pressure of the cushioning member for the seat cushion stretched across the cushion frame, a movable frame horizontally and pivotably fixed on a front side of the cushion frame, characterized by a torsion bar horizontally hung on in the rear of the cushion frame; and a rear end supporting frame serving as a portion of the cushion frame and hung on parallel to and downward from the torsion bar via L-shaped arms using both ends of the torsion bar as a rotational center; wherein one end of the cloth spring is disposed on the front of said cushion frame along the width direction and engaged with the moveable frame and the other end of the cloth spring is connected to the rear end supporting frame; and wherein said cloth spring adjusting member is configured to pivot said movable frame in front and behind, wherein at least a portion of said cushioning member for the seat cushion is displaced in a direction protruding upward to raise the supporting pressure by pivoting the movable frame forward in the seated state to adjust the tension of the cloth spring. a supporting pressure adjusting means for the seat cushion for changing a supporting pressure of the cushioning member for the seat cushion, wherein the supporting pressure adjusting means for the seat cushion comprises: a cloth spring provided on the back of the cushioning member for the seat cushion and stretched across the cushion frame; and a cloth spring adjusting member to adjust tension of the cloth spring, wherein said cloth spring adjusting member adjusts the tension of the cloth spring to change the supporting pressure of the cushioning member for the seat cushion stretched across the cushion frame, a movable frame horizontally and pivotably fixed on a front side of the cushion frame, characterized by a torsion bar horizontally hung on in the rear of the cushion frame; and a rear end supporting frame serving as a portion of the cushion frame and hung on parallel to and downward from the torsion bar via L-shaped arms using both ends of the torsion bar as a rotational center; wherein one end of the cloth spring is disposed on the front of said cushion frame along the width direction and engaged with the moveable frame and the other end of the cloth spring is connected to the rear end supporting frame; and wherein said cloth spring adjusting member is configured to pivot said movable frame in front and behind, wherein at least a portion of said cushioning member for the seat cushion is displaced in a direction protruding upward to raise the supporting pressure by pivoting the movable frame forward in the seated state to adjust the tension of the cloth spring. a cloth spring provided on the back of the cushioning member for the seat cushion and stretched across the cushion frame; and a cloth spring adjusting member to adjust tension of the cloth spring, wherein said cloth spring adjusting member adjusts the tension of the cloth spring to change the supporting pressure of the cushioning member for the seat cushion stretched across the cushion frame, a movable frame horizontally and pivotably fixed on a front side of the cushion frame, characterized by a torsion bar horizontally hung on in the rear of the cushion frame; and a rear end supporting frame serving as a portion of the cushion frame and hung on parallel to and downward from the torsion bar via L-shaped arms using both ends of the torsion bar as a rotational center; wherein one end of the cloth spring is disposed on the front of said cushion frame along the width direction and engaged with the moveable frame and the other end of the cloth spring is connected to the rear end supporting frame; and wherein said cloth spring adjusting member is configured to pivot said movable frame in front and behind, wherein at least a portion of said cushioning member for the seat cushion is displaced in a direction protruding upward to raise the supporting pressure by pivoting the movable frame forward in the seated state to adjust the tension of the cloth spring.