A sparkplug comprising: an insulator having an axial hole extending along an axial line O; a center electrode inserted in the axial hole; a metal shell disposed in or at an outer circumference of the insulator; and a ground electrode disposed in or at a front end of the metal shell, wherein a shelf part protruding inward in a radial direction is formed on an inner circumference of the metal shell, wherein the insulator includes: a first column part formed in a position facing at least a part of the shelf part; a taper part formed in or at a front end side of the first column part and having a diameter decreasing toward the front end side; and a second column part formed in or at the front end side of the taper part, characterized in that, when a volume of the insulator surrounded by a first plane PS1 that passes through the front end of the shelf part of the metal shell and is orthogonal to the axial line O, a curved surface CS extending from an outer circumference of the second column part, and an outer circumference surface of the insulator is defined as A, and a volume of the insulator surrounded by the first plane PS1, the curved surface CS, a second plane PS2 that passes through the front end of the metal shell and is orthogonal to the axial line O, and the axial hole of the insulator is defined as B, a relational expression 0.9 ≤ A / B ≤ 2.4 is satisfied. an insulator having an axial hole extending along an axial line O; a center electrode inserted in the axial hole; a metal shell disposed in or at an outer circumference of the insulator; and a ground electrode disposed in or at a front end of the metal shell, wherein a shelf part protruding inward in a radial direction is formed on an inner circumference of the metal shell, wherein the insulator includes: a first column part formed in a position facing at least a part of the shelf part; a taper part formed in or at a front end side of the first column part and having a diameter decreasing toward the front end side; and a second column part formed in or at the front end side of the taper part, characterized in that, when a volume of the insulator surrounded by a first plane PS1 that passes through the front end of the shelf part of the metal shell and is orthogonal to the axial line O, a curved surface CS extending from an outer circumference of the second column part, and an outer circumference surface of the insulator is defined as A, and a volume of the insulator surrounded by the first plane PS1, the curved surface CS, a second plane PS2 that passes through the front end of the metal shell and is orthogonal to the axial line O, and the axial hole of the insulator is defined as B, a relational expression 0.9 ≤ A / B ≤ 2.4 is satisfied. a first column part formed in a position facing at least a part of the shelf part; a taper part formed in or at a front end side of the first column part and having a diameter decreasing toward the front end side; and a second column part formed in or at the front end side of the taper part, characterized in that, when a volume of the insulator surrounded by a first plane PS1 that passes through the front end of the shelf part of the metal shell and is orthogonal to the axial line O, a curved surface CS extending from an outer circumference of the second column part, and an outer circumference surface of the insulator is defined as A, and a volume of the insulator surrounded by the first plane PS1, the curved surface CS, a second plane PS2 that passes through the front end of the metal shell and is orthogonal to the axial line O, and the axial hole of the insulator is defined as B, a relational expression 0.9 ≤ A / B ≤ 2.4 is satisfied.