A battery charging device that is connected between a three-phase alternating current generator having U, V, and W phases and a battery, and is constructed so as to convert alternating current power output from the three-phase alternating current generator into direct current power and supply the direct current power to the battery, and that performs advance angle/delay angle control by either advancing or delaying an energization timing to switching elements (Q1-Q6) of a rectifier portion having a bridge configuration relative to a phase of the alternating current output voltage from the three-phase alternating current generator, the device comprising an advance angle/delay angle control circuit that performs the advance angle/delay angle control of the switching elements (Q1-Q6), characterized by further comprising: an alternating current output voltage detection circuit (Su) that detects an alternating current output voltage of any one phase of the three-phase alternating current generator; a U, V, W phase voltage generating circuit that generates a synchronous signal that is in synchronization with an alternating current output voltage of the one phase that is detected by the alternating current output voltage detection circuit (Su), and detects positions of the other two phases with taking the synchronous signal of the one phase as a reference to generate synchronous signals of the other two phases; and an advance angle/delay angle calculation circuit that compares a signal of a differential voltage between a voltage of the battery and a predetermined target voltage with triangular waves that are in synchronization with the synchronous signals of each phase that are output by the U, V, W phase voltage generating circuit to determine an advance angle/delay angle amount of the energization timing to the switching elements (Q1-Q6), wherein the advance angle/delay angle control circuit performs the advance angle/delay angle control of the switching elements (Q1-Q6) using the advance angle/delay angle amount determined by the advance angle/delay angle calculation circuit. an alternating current output voltage detection circuit (Su) that detects an alternating current output voltage of any one phase of the three-phase alternating current generator; a U, V, W phase voltage generating circuit that generates a synchronous signal that is in synchronization with an alternating current output voltage of the one phase that is detected by the alternating current output voltage detection circuit (Su), and detects positions of the other two phases with taking the synchronous signal of the one phase as a reference to generate synchronous signals of the other two phases; and an advance angle/delay angle calculation circuit that compares a signal of a differential voltage between a voltage of the battery and a predetermined target voltage with triangular waves that are in synchronization with the synchronous signals of each phase that are output by the U, V, W phase voltage generating circuit to determine an advance angle/delay angle amount of the energization timing to the switching elements (Q1-Q6), wherein the advance angle/delay angle control circuit performs the advance angle/delay angle control of the switching elements (Q1-Q6) using the advance angle/delay angle amount determined by the advance angle/delay angle calculation circuit.