In a front fork which is capable of adjusting a spring force of a suspension spring housed in a fork main body by driving a jack mechanism housed in the fork main body to raise and lower an upper end position of the suspension spring, the jack mechanism defines a pressure chamber by means of a cap member that closes an upper end opening of a vehicle body side tube and a piston member. By supplying and discharging a pressure oil to and from the pressure chamber, the piston member ascends and descends, thereby raising and lowering the upper end position of the suspension spring.