A shock absorber includes a bypass passage that is open from the side of a piston rod and causes an extension side chamber and a compression side chamber, which are divided by a piston in a cylinder, to communicate with each other; a shutter that is mounted on an outer circumference of the piston rod to be movable in an axial direction and opens or closes the bypass passage; and a coil spring that connects a rod guide mounted on one end portion of the cylinder and the shutter.