There are provided a ceramic heater in which a defect, such as generation of a gap at the interface between an insulating substrate and a heat-generating resistor, is unlikely to occur in the course of manufacture or use, and a glow plug using the ceramic heater. A ceramic heater 110 includes an insulating substrate 111 extending in the direction of an axis AX and a heat-generating resistor 115, which has a heat-generating portion 116, two lead portions 117, 117 and two lead lead-out portions 118a and 118b. The ceramic heater 110 satisfies an expression S1≦0.34 Sa, where Sa is the area of a cross section of the ceramic heater 110 taken perpendicular to the direction of the axis AX, and S1 is the total cross-sectional area of the two lead portions 117, 117 as measured in the cross section.