To provide a shock absorber for preventing a door body of a gate provided at an opening end of a water channel from being struck strongly on the opening end, and a gate with the same.

The structure of a shock absorber 20 comprises a cylindrical cylinder 21, a rod 23 where a piston 24 is formed, and a control part 22 provided at the cylinder 21, and the inside is filled with a viscous fluid 27 such as oil. The shock absorber 20 is provided with two kinds of a flow passage 25 and a flow passage 26 so as to connect an internal space A and an internal space B, partitioned off with the piston 24, to each other. The control part 22 is provided with a flow passage 25 and a valve 29 is inserted into a throttle part 28 provided in the flow passage 25. The throttle part 28 is closed in an arbitrary timing by adjusting a push spring 30 provided at one end of the valve 29, a spring strength adjusting screw 31, and an opening adjusting screw 32 provided at the other end of the valve 29 so as to control the flow rate of a viscous fluid 27 flowing in the flow passage 25.