A ceramic heater (12) includes a substrate (60) and a resistor element (30) buried in the substrate (60). The resistor element (30) includes a heat-generating portion (33), lead portions (31), and intermediate portions (40) located between the heat-generating portions (33) and the lead portions (31). The intermediate portions (40) are formed such that, when cross sections at arbitrary two points P1 and P2 along the axis XA direction are compared, both the diameter CL of an imaginary circumscribed circle CG containing cross sections of the resistor element 30 and the total cross sectional area HS of the cross sections become small in the front end side cross section as compared with those in the rear end side cross section.