Booster seat

A booster seat has a seat member (14) and armrests (12a, 13a). The distance between the armrests (12a, 13a) can be automatically changed according to the height of the support portion (14a) of the seat member (14). The armrests (12a, 13a) are formed on side members (12, 13) extended on the opposite sides of the support portion (14a) of the seat member 14 on a base (11) mounted on a seat of a vehicle. A plurality of tapered, wedge-shaped blocks (17, 18) are arranged on the inner side surfaces of the side members (12, 13) so as to extend toward a middle portion of the support portion (14a). The wedge-shaped blocks (17, 18) extend from the inner side surfaces of the side members (12, 13) toward each other. The wedge-shaped blocks (17, 18) have sloping upper surfaces (17a, 18a). The seat member 14 is placed on the upper surfaces (17a, 18a) of the wedge-shaped blocks (17, 18). A bottom portion of the seat member (14) facing the wedge-shaped blocks (17, 18) has a V-shaped bottom surface (14b) corresponding to the upper surfaces (17a, 18a). When the side members (12, 13) and the wedge-shaped blocks (17, 18) are moved on the base (11) in directions along the width of the support portion (14a), the seat member (14) is moved vertically relative to the base (11) by the cooperative action of the upper surfaces (17a, 18a) of the wedge-shaped blocks (17, 18) and the bottom surface (14b) of the seat member (14) and, at the same time, the distance between the armrests (12a, 13a) is adjusted.