An electric heater comprising: a substrate; and a plane heating element (100, 200 and 300) formed on one surface of the substrate, wherein the plane heating element (100, 200 and 300) includes: a pattern portion (110, 210 and 310) connecting a start point and an end point thereof, which are located at the outermost side, wherein the pattern portion (110, 210 and 310) includes: a plurality of tracks (111, 211 and 311) having an arc shape, which are spaced apart from each other and are formed to have a length increasing from the inside to the outside, and a plurality of bridges (112, 212 and 312) connecting the tracks (111, 211 and 311) in series, and wherein the bridges (112, 212 and 312) are formed on both sides with respect to a reference line (B/L) passing through the center of the pattern portion (110, 210 and 310), and an innermost gap (G in) between a pair of bridges (112, 212 and 312) located at the innermost side of the pattern portion (110, 210 and 310) and facing each other about the reference line B/L is configured to be shorter than an outermost gap (G out) between another pair of bridges (112, 212 and 312) located at the outermost side of the pattern portion (110, 210 and 310) and facing each other about the reference line (B/L), characterized in that a gap between a pair of bridges (112, 212 and 312) facing each other about the reference line (B/L) is configured to have a length increasing from the innermost side to the outermost side of the pattern portion (110, 210 and 310). a substrate; and a plane heating element (100, 200 and 300) formed on one surface of the substrate, wherein the plane heating element (100, 200 and 300) includes: a pattern portion (110, 210 and 310) connecting a start point and an end point thereof, which are located at the outermost side, wherein the pattern portion (110, 210 and 310) includes: a plurality of tracks (111, 211 and 311) having an arc shape, which are spaced apart from each other and are formed to have a length increasing from the inside to the outside, and a plurality of bridges (112, 212 and 312) connecting the tracks (111, 211 and 311) in series, and a plurality of tracks (111, 211 and 311) having an arc shape, which are spaced apart from each other and are formed to have a length increasing from the inside to the outside, and a plurality of bridges (112, 212 and 312) connecting the tracks (111, 211 and 311) in series, and wherein the bridges (112, 212 and 312) are formed on both sides with respect to a reference line (B/L) passing through the center of the pattern portion (110, 210 and 310), and an innermost gap (G in) between a pair of bridges (112, 212 and 312) located at the innermost side of the pattern portion (110, 210 and 310) and facing each other about the reference line B/L is configured to be shorter than an outermost gap (G out) between another pair of bridges (112, 212 and 312) located at the outermost side of the pattern portion (110, 210 and 310) and facing each other about the reference line (B/L), characterized in that a gap between a pair of bridges (112, 212 and 312) facing each other about the reference line (B/L) is configured to have a length increasing from the innermost side to the outermost side of the pattern portion (110, 210 and 310).