A spark plug comprising: a center electrode and a ground electrode having a gap between the center electrode and the ground electrode, wherein the ground electrode has at least a core portion and an outer layer covering the core portion, the core portion is formed from a material having higher thermal conductivity than that of the outer layer, at least a portion in which thickness of the outer layer is 0.5 mm or less exists at a cross-section perpendicular to a direction in which the ground electrode is extended, characterized in that the composition of electrode material forming the outer layer is as follows: Ni is 96 mass% or more; total of at least one kind selected from a group consisting of Y and rare earth elements is 0.05 mass% or more; Al is 0.5 mass% or less; Si is 0.5 mass% or more and 1.5 mass% or less; Mn is 0.05 mass% or more; and inevitable impurities; wherein total of at least one kind selected from an element group A consisting of Ti, V, and Nb is 0.01 mass% or more, and ratio (a/b) between the content (b) of Mn and total content (a) of the element group A is 0.02 or more and 0.40 or less in the composition of the electrode material and optionally C is 0.001 mass% or more and 0.1 mass% or less, and/or at least one or two kinds selected from a group consisting of Cr of 0.01 mass% or more and 0.5 mass% or less; Mn of 0.05 mass% or more and 2.5 mass% or less; and Ti of 0.01 mass% or more and 0.5 mass% or less. a center electrode and a ground electrode having a gap between the center electrode and the ground electrode, wherein the ground electrode has at least a core portion and an outer layer covering the core portion, the core portion is formed from a material having higher thermal conductivity than that of the outer layer, at least a portion in which thickness of the outer layer is 0.5 mm or less exists at a cross-section perpendicular to a direction in which the ground electrode is extended, characterized in that the composition of electrode material forming the outer layer is as follows: Ni is 96 mass% or more; total of at least one kind selected from a group consisting of Y and rare earth elements is 0.05 mass% or more; Al is 0.5 mass% or less; Si is 0.5 mass% or more and 1.5 mass% or less; Mn is 0.05 mass% or more; and inevitable impurities; wherein total of at least one kind selected from an element group A consisting of Ti, V, and Nb is 0.01 mass% or more, and ratio (a/b) between the content (b) of Mn and total content (a) of the element group A is 0.02 or more and 0.40 or less in the composition of the electrode material and optionally C is 0.001 mass% or more and 0.1 mass% or less, and/or at least one or two kinds selected from a group consisting of Cr of 0.01 mass% or more and 0.5 mass% or less; Mn of 0.05 mass% or more and 2.5 mass% or less; and Ti of 0.01 mass% or more and 0.5 mass% or less. Ni is 96 mass% or more; total of at least one kind selected from a group consisting of Y and rare earth elements is 0.05 mass% or more; Al is 0.5 mass% or less; Si is 0.5 mass% or more and 1.5 mass% or less; Mn is 0.05 mass% or more; and inevitable impurities; wherein total of at least one kind selected from an element group A consisting of Ti, V, and Nb is 0.01 mass% or more, and ratio (a/b) between the content (b) of Mn and total content (a) of the element group A is 0.02 or more and 0.40 or less in the composition of the electrode material and optionally C is 0.001 mass% or more and 0.1 mass% or less, and/or at least one or two kinds selected from a group consisting of Cr of 0.01 mass% or more and 0.5 mass% or less; Mn of 0.05 mass% or more and 2.5 mass% or less; and Ti of 0.01 mass% or more and 0.5 mass% or less.