A damping force variable shock absorber comprising: a cylinder in which fluid is enclosed; a piston slidably fitted into the cylinder; a piston rod having one end connected to the piston and the other end extended outside the cylinder; a rod-side fluid chamber partitioned by the piston and provided closer to the other end in an axial direction of the cylinder than the piston; a piston-side fluid chamber provided closer to one end in the axial direction of the cylinder than the piston; and a damping force variable device that controls flow of the fluid enclosed in the cylinder so that damping force can be varied, wherein the damping force variable device includes: a main valve that opens and closes to control the flow of the fluid caused by sliding of the piston in the cylinder, thereby generating damping force; a pilot chamber into which a portion of the flow of the fluid is introduced so that internal pressure is applied to the main valve in a valve-closing direction; and a pilot valve that opens and closes to adjust the internal pressure of the pilot chamber; characterized in that the damping force variable device includes a communication passage that allows the pilot chamber or a passage between the pilot chamber and the pilot valve to communicate with the rod-side fluid chamber or the piston-side fluid chamber, and when the communication passage allows the pilot chamber or the passage between the pilot chamber and the pilot valve to communicate with the rod-side fluid chamber, one end of the communication passage is open to a gap formed between the cylinder and the piston and communicating with the rod-side chamber, or when the communication passage allows the pilot chamber or the passage between the pilot chamber and the pilot valve to communicate with the piston-side fluid chamber, one end of the communication passage is open to a gap formed between the cylinder and the piston and communicating with the piston-side chamber. a cylinder in which fluid is enclosed; a piston slidably fitted into the cylinder; a piston rod having one end connected to the piston and the other end extended outside the cylinder; a rod-side fluid chamber partitioned by the piston and provided closer to the other end in an axial direction of the cylinder than the piston; a piston-side fluid chamber provided closer to one end in the axial direction of the cylinder than the piston; and a damping force variable device that controls flow of the fluid enclosed in the cylinder so that damping force can be varied, wherein the damping force variable device includes: a main valve that opens and closes to control the flow of the fluid caused by sliding of the piston in the cylinder, thereby generating damping force; a pilot chamber into which a portion of the flow of the fluid is introduced so that internal pressure is applied to the main valve in a valve-closing direction; and a pilot valve that opens and closes to adjust the internal pressure of the pilot chamber; a main valve that opens and closes to control the flow of the fluid caused by sliding of the piston in the cylinder, thereby generating damping force; a pilot chamber into which a portion of the flow of the fluid is introduced so that internal pressure is applied to the main valve in a valve-closing direction; and a pilot valve that opens and closes to adjust the internal pressure of the pilot chamber; the damping force variable device includes a communication passage that allows the pilot chamber or a passage between the pilot chamber and the pilot valve to communicate with the rod-side fluid chamber or the piston-side fluid chamber, and when the communication passage allows the pilot chamber or the passage between the pilot chamber and the pilot valve to communicate with the rod-side fluid chamber, one end of the communication passage is open to a gap formed between the cylinder and the piston and communicating with the rod-side chamber, or when the communication passage allows the pilot chamber or the passage between the pilot chamber and the pilot valve to communicate with the piston-side fluid chamber, one end of the communication passage is open to a gap formed between the cylinder and the piston and communicating with the piston-side chamber.