Disclosed is a variable damping force shock absorber including a tube cylinder having an inner tube filled with a fluid and an outer tube, a valve housing coupled to a piston rod in the inner tube and having a connection flow path formed therein, a first piston valve coupled to the outside of the valve housing to partition the inner tube into a compression chamber and a rebound chamber, and a second piston valve provided inside the valve housing, wherein the valve housing includes a magnet provided at an upper portion thereof and connected to the piston rod, and a plunger disposed between the magnet and the second piston valve at a lower portion thereof to selectively open and close the connection flow path by a magnetic field of the magnet, and wherein the fluid passes only through the first piston valve when the plunger closes the connection flow path, and the fluid passes through the first piston valve and the second piston valve when the plunger opens the connection flow path.