An oxygen sensor control apparatus includes internal resistance detection means S3, controlled internal resistance obtaining means S4 to S11, and heater energization control means S12. When a timing for detecting the internal resistance R(n) comes during a lean period TL, the controlled internal resistance obtaining means uses the detected internal resistance R(n) as the controlled internal resistance Rf. When a timing for detecting the internal resistance R(n) comes during a rich period TR, the controlled internal resistance obtaining means uses, as the controlled internal resistance Rf, a value obtained by correcting the detected internal resistance R(n) on the basis of a latest lean resistance R(k) such that a variation of the internal resistance which stems from the difference between the lean state and the rich state and which is contained in the detected internal resistance R(n) is removed.