A glow plug comprising: a heater that generates heat by energization; a main metal shell having a tubular shape with a shaft hole _ and retaining the heater directly or indirectly on a front end side in an axial direction extending along its own axis; a metal conductive member having electrical continuity with one terminal of the heater and extending in the shaft hole toward a rear end side in the axial direction; a metal terminal member with one part positioned in the shaft hole and another part protruding from a rear end of the main metal shell toward the rear end side in the axial direction, the terminal member including an enclosing portion opened toward the front end side in the axial direction, the enclosing portion housing a rear end portion of the conductive member and having electrical continuity with the rear end portion, the terminal member being disposed in the shaft hole while spaced apart from an inner peripheral surface of the main metal shell forming the shaft hole; a sealing member made of an insulator and airtightly sealing and insulating between the inner peripheral surface and the terminal member in the shaft hole; an insulating spacer made of an insulator and positioned on the rear end side of the sealing member in the axial direction between the inner peripheral surface and the terminal member, wherein the terminal member includes a spacer engaging portion and is engaged with the insulating spacer at the spacer engaging portion, and wherein the insulating spacer is biased toward the front end side in the axial direction; the glow plug characterized by the terminal member including a tubular enclosing portion having a bottom end opened toward the front end side along the axial direction, the enclosing portion housing the rear end portion of the conductive member and airtightly covering the rear end portion radially circumferentially and from the rear end side, wherein the rear end portion of the conductive member protrudes from the rear end surface of the main metal shell. a heater that generates heat by energization; a main metal shell having a tubular shape with a shaft hole _ and retaining the heater directly or indirectly on a front end side in an axial direction extending along its own axis; a metal conductive member having electrical continuity with one terminal of the heater and extending in the shaft hole toward a rear end side in the axial direction; a metal terminal member with one part positioned in the shaft hole and another part protruding from a rear end of the main metal shell toward the rear end side in the axial direction, the terminal member including an enclosing portion opened toward the front end side in the axial direction, the enclosing portion housing a rear end portion of the conductive member and having electrical continuity with the rear end portion, the terminal member being disposed in the shaft hole while spaced apart from an inner peripheral surface of the main metal shell forming the shaft hole; a sealing member made of an insulator and airtightly sealing and insulating between the inner peripheral surface and the terminal member in the shaft hole; an insulating spacer made of an insulator and positioned on the rear end side of the sealing member in the axial direction between the inner peripheral surface and the terminal member, wherein the terminal member includes a spacer engaging portion and is engaged with the insulating spacer at the spacer engaging portion, and wherein the insulating spacer is biased toward the front end side in the axial direction;