A spark plug comprising: a center electrode; and a ground electrode disposed so as to form a gap between the center electrode and the ground electrode, wherein at least one of the center electrode and the ground electrode includes an electrode body (21, 31), an electrode tip (29, 39) having a discharge surface (295, 395) that faces the gap, and a welded portion (25, 35) formed between the electrode body (21, 31) and the electrode tip (29, 39) and containing a component of the electrode body (21, 31) and a component of the electrode tip (29, 39), the electrode tip (29, 39) includes: a tip body (27, 37) comprising a side surface extending in a direction that intersects the discharge surface (295, 395), and an opposite surface (271, 371) which is disposed on an opposite side of the discharge surface (295, 395), at least a part of which is in contact with the welded portion (25, 35) and a part of which is a non-contact portion (271A, 371A) not in contact with the welded portion (25, 35) and a cover layer (28, 38) that covers at least the side surface of the tip body (27, 37), the tip body (27, 37) comprises iridium (Ir) or an alloy containing iridium (Ir) as a main component, the cover layer (28, 38) comprises an intermetallic compound (IrAl) of iridium (Ir) and aluminum (Al) and having a thickness of 50 μm or less, the electrode body (21, 31) comprises an alloy containing 50% by weight or more of nickel (Ni), and wherein "Sa" is defined as an area of a section through the tip body (27, 37) along a plane located near but not intersecting the welded portion (25, 35), and parallel to the discharge surface (295, 395), wherein "Sb" is defined as an area of a projection of the non-contact portion (271A, 371A) of the opposite surface (271, 371) on the section in a direction perpendicular to the discharge surface (295, 395), characterized in that Sa - Sb corresponds to 35% or more of Sa, and a content of aluminum (Al) in the welded portion (25, 35) in a vicinity of a boundary between the tip body (27, 37) and the welded portion (25, 35) is 10% by mass or less. a center electrode; and a ground electrode disposed so as to form a gap between the center electrode and the ground electrode, wherein at least one of the center electrode and the ground electrode includes an electrode body (21, 31), an electrode tip (29, 39) having a discharge surface (295, 395) that faces the gap, and a welded portion (25, 35) formed between the electrode body (21, 31) and the electrode tip (29, 39) and containing a component of the electrode body (21, 31) and a component of the electrode tip (29, 39), the electrode tip (29, 39) includes: a tip body (27, 37) comprising a side surface extending in a direction that intersects the discharge surface (295, 395), and an opposite surface (271, 371) which is disposed on an opposite side of the discharge surface (295, 395), at least a part of which is in contact with the welded portion (25, 35) and a part of which is a non-contact portion (271A, 371A) not in contact with the welded portion (25, 35) and a cover layer (28, 38) that covers at least the side surface of the tip body (27, 37), the tip body (27, 37) comprises iridium (Ir) or an alloy containing iridium (Ir) as a main component, the cover layer (28, 38) comprises an intermetallic compound (IrAl) of iridium (Ir) and aluminum (Al) and having a thickness of 50 μm or less, the electrode body (21, 31) comprises an alloy containing 50% by weight or more of nickel (Ni), and wherein "Sa" is defined as an area of a section through the tip body (27, 37) along a plane located near but not intersecting the welded portion (25, 35), and parallel to the discharge surface (295, 395), wherein "Sb" is defined as an area of a projection of the non-contact portion (271A, 371A) of the opposite surface (271, 371) on the section in a direction perpendicular to the discharge surface (295, 395), characterized in that Sa - Sb corresponds to 35% or more of Sa, and a content of aluminum (Al) in the welded portion (25, 35) in a vicinity of a boundary between the tip body (27, 37) and the welded portion (25, 35) is 10% by mass or less. a tip body (27, 37) comprising a side surface extending in a direction that intersects the discharge surface (295, 395), and an opposite surface (271, 371) which is disposed on an opposite side of the discharge surface (295, 395), at least a part of which is in contact with the welded portion (25, 35) and a part of which is a non-contact portion (271A, 371A) not in contact with the welded portion (25, 35) and a cover layer (28, 38) that covers at least the side surface of the tip body (27, 37), the tip body (27, 37) comprises iridium (Ir) or an alloy containing iridium (Ir) as a main component, the cover layer (28, 38) comprises an intermetallic compound (IrAl) of iridium (Ir) and aluminum (Al) and having a thickness of 50 μm or less, the electrode body (21, 31) comprises an alloy containing 50% by weight or more of nickel (Ni), and wherein "Sa" is defined as an area of a section through the tip body (27, 37) along a plane located near but not intersecting the welded portion (25, 35), and parallel to the discharge surface (295, 395), wherein "Sb" is defined as an area of a projection of the non-contact portion (271A, 371A) of the opposite surface (271, 371) on the section in a direction perpendicular to the discharge surface (295, 395), characterized in that Sa - Sb corresponds to 35% or more of Sa, and a content of aluminum (Al) in the welded portion (25, 35) in a vicinity of a boundary between the tip body (27, 37) and the welded portion (25, 35) is 10% by mass or less.