A battery charging apparatus for a vehicle comprising: a position sensor configured to output a position detection signal (Tp) that expresses a rotation position of a rotor of a three-phase AC generator; a sensor; a regulator that includes a plurality of rectifying elements and a plurality of switching elements and is configured to supply DC power obtained by rectifying three-phase AC outputted from the three-phase AC generator to a battery; and a control circuit configured to execute energization control of the respective switching elements of the regulator based on the phase of the induced voltage on a predetermined phase of the three-phase AC generator calculated on the basis of the position detection signal; and characterized in that the sensor is configured to detect an output current or an output voltage of the predetermined phase of the three-phase AC generator when the control circuit suspends the energization control or when the control circuit executes all phase short circuits in the energization control; wherein the control circuit includes: input means configured to receive the position detection signal (Tp) and a battery terminal voltage (Vbatt); that the input means is configured to further receive a revolution speed signal (Ne) showing the revolution speed of the three-phase AC generator, and an output signal consisting of the output current signal or of the output voltage signal detected by the sensor; and that the control circuit further includes measurement means configured to measure a first phase difference (Δθ1) between the position detection signal (Tp) and the output signal (I1 or V2); calculation means configured to calculate a second phase difference (Δθ2) between the induced voltage of the predetermined phase and the output signal (II or V2) by using a correction map which outputs the value of the second phase difference (Δθ2) based on the revolution speed signal (Ne) and the battery terminal voltage (Vbatt); and estimate means configured to estimate a third phase difference (Δθ3) between the position detection signal and the induced voltage of the predetermined phase from the difference between the first and the second phase difference (Δθ1, Δθ2). a position sensor configured to output a position detection signal (Tp) that expresses a rotation position of a rotor of a three-phase AC generator; a sensor; a regulator that includes a plurality of rectifying elements and a plurality of switching elements and is configured to supply DC power obtained by rectifying three-phase AC outputted from the three-phase AC generator to a battery; and a control circuit configured to execute energization control of the respective switching elements of the regulator based on the phase of the induced voltage on a predetermined phase of the three-phase AC generator calculated on the basis of the position detection signal; and that the sensor is configured to detect an output current or an output voltage of the predetermined phase of the three-phase AC generator when the control circuit suspends the energization control or when the control circuit executes all phase short circuits in the energization control; wherein the control circuit includes: input means configured to receive the position detection signal (Tp) and a battery terminal voltage (Vbatt); that the input means is configured to further receive a revolution speed signal (Ne) showing the revolution speed of the three-phase AC generator, and an output signal consisting of the output current signal or of the output voltage signal detected by the sensor; and that the control circuit further includes measurement means configured to measure a first phase difference (Δθ1) between the position detection signal (Tp) and the output signal (I1 or V2); calculation means configured to calculate a second phase difference (Δθ2) between the induced voltage of the predetermined phase and the output signal (II or V2) by using a correction map which outputs the value of the second phase difference (Δθ2) based on the revolution speed signal (Ne) and the battery terminal voltage (Vbatt); and estimate means configured to estimate a third phase difference (Δθ3) between the position detection signal and the induced voltage of the predetermined phase from the difference between the first and the second phase difference (Δθ1, Δθ2).