A ceramic heater comprising: a resistor which generates heat when energized; and a base member which extends along an axial direction and in which the resistor is embedded, the base member being formed of a ceramic material which is lower in electrical conductivity than the resistor, wherein the resistor includes a first portion extending from a forward end portion of the base member toward a rear end portion thereof, a second portion spaced from the first portion and extending from the forward end portion of the base member toward the rear end portion thereof, and a connection portion embedded in the forward end portion of the base member and connecting the first portion and the second portion; and in a cross section of the ceramic heater taken orthogonal to the axial direction, a first resistor cross section taken through the first portion of the resistor and a second resistor cross section taken through the second portion of the resistor, the first cross-section being spaced from the second cross-section, with two straight lines (L1, L2) which are in contact with both a peripheral contour (C1L) of the first resistor cross section and a peripheral contour (C2L) of the second resistor cross section and which pass between the first resistor cross section and the second resistor cross section in the cross section of the ceramic heater being defined as a first straight line and a second straight line, wherein each of the straight lines (L1, L2) is tangential to both of the contour (C1L) of the first resistor cross section and the contour (C2L) of the second resistor cross section, characterized in that the first resistor cross section has no protrusion on a first inner portion, the first inner portion being a portion of the contour (C1L) of the first resistor cross section located on the side toward the second resistor cross section, the first inner portion extending from a first position at which the contour (C1L) is in contact with the first straight line to a second position at which the contour is in contact with the second straight line, and the first resistor cross section has two or more protrusions (B11v, B12v) on a first outer portion, the first outer portion being a portion of the contour (C1L) of the first resistor cross section located on the side opposite the second resistor cross section, the first outer portion extending from the first position to the second position. a resistor which generates heat when energized; and a base member which extends along an axial direction and in which the resistor is embedded, the base member being formed of a ceramic material which is lower in electrical conductivity than the resistor, wherein the resistor includes a first portion extending from a forward end portion of the base member toward a rear end portion thereof, a second portion spaced from the first portion and extending from the forward end portion of the base member toward the rear end portion thereof, and a connection portion embedded in the forward end portion of the base member and connecting the first portion and the second portion; and in a cross section of the ceramic heater taken orthogonal to the axial direction, a first resistor cross section taken through the first portion of the resistor and a second resistor cross section taken through the second portion of the resistor, the first cross-section being spaced from the second cross-section, with two straight lines (L1, L2) which are in contact with both a peripheral contour (C1L) of the first resistor cross section and a peripheral contour (C2L) of the second resistor cross section and which pass between the first resistor cross section and the second resistor cross section in the cross section of the ceramic heater being defined as a first straight line and a second straight line, wherein each of the straight lines (L1, L2) is tangential to both of the contour (C1L) of the first resistor cross section and the contour (C2L) of the second resistor cross section, characterized in that the first resistor cross section has no protrusion on a first inner portion, the first inner portion being a portion of the contour (C1L) of the first resistor cross section located on the side toward the second resistor cross section, the first inner portion extending from a first position at which the contour (C1L) is in contact with the first straight line to a second position at which the contour is in contact with the second straight line, and the first resistor cross section has two or more protrusions (B11v, B12v) on a first outer portion, the first outer portion being a portion of the contour (C1L) of the first resistor cross section located on the side opposite the second resistor cross section, the first outer portion extending from the first position to the second position.