Disclosed is a spark plug which reinforces adhesiveness of a resistor and a conductive glass sealing layer, and is superior in vibration resistance property and a resistor load life characteristic and whose size is made small. The resistor (18) and a center electrode (13), which are arranged in a through hole (16) of an insulator (12), are bonded by the conductive glass sealing layer (19) arranged in-between. A diameter D of the conductive glass sealing layer (19) bonded to the resistor (18) is 1.9mm to 3.3mm (1.9mm = D = 3.3mm), and a bonding face (23) of the conductive glass sealing layer (19) bonded to the resistor (18) is formed in a bowl shape. Sa/S1 obtained based on a surface area Sa of the bonding face (23) and a cross-section area S1 of the conductive glass sealing layer (19) is not less than 1.1 (Sa/S1 = 1.1).
