A power supply apparatus, comprising: a power supply; a drive circuit for receiving supply of power from said power supply and driving a load circuit, said load circuit including an AC motor; and an abnormal current detection circuit for detecting abnormality in a drive current flowing through said drive circuit; said abnormal current detection circuit including current detection means for detecting a maximum value of said drive current for each prescribed operation cycle, and abnormality determination means for determining whether the maximum value of said drive current exceeds a prescribed threshold value for each said prescribed operation cycle, said abnormality determination means is adapted to determine presence of abnormality in said drive current when detecting that the maximum value of said drive current exceeds said prescribed threshold value in each of n consecutive cycles of said prescribed operation cycles, n being a natural number of at least 3, characterized in that said power supply apparatus further comprises a mode determination means for determining a control mode of said AC motor, said mode determination means being adapted to determine one of control modes having different carrier frequencies, and said abnormality determination means ( 62a; 62b; 62c) is adapted to adjust said prescribed threshold value to a threshold value suitable for the determined control mode by adjusting said threshold value in accordance with the carrier frequency of said determined control mode, to determine whether the detected maximum value of said drive current exceeds said suitable threshold value for each said prescribed operation cycle, and to determine presence of abnormality in said drive current when detecting that the maximum value of said drive current exceeds said suitable threshold value in each of said n consecutive prescribed operation cycles. a power supply; a drive circuit for receiving supply of power from said power supply and driving a load circuit, said load circuit including an AC motor; and an abnormal current detection circuit for detecting abnormality in a drive current flowing through said drive circuit; said abnormal current detection circuit including current detection means for detecting a maximum value of said drive current for each prescribed operation cycle, and abnormality determination means for determining whether the maximum value of said drive current exceeds a prescribed threshold value for each said prescribed operation cycle, said abnormality determination means is adapted to determine presence of abnormality in said drive current when detecting that the maximum value of said drive current exceeds said prescribed threshold value in each of n consecutive cycles of said prescribed operation cycles, n being a natural number of at least 3, said power supply apparatus further comprises a mode determination means for determining a control mode of said AC motor, said mode determination means being adapted to determine one of control modes having different carrier frequencies, and said abnormality determination means ( 62a; 62b; 62c) is adapted to adjust said prescribed threshold value to a threshold value suitable for the determined control mode by adjusting said threshold value in accordance with the carrier frequency of said determined control mode, to determine whether the detected maximum value of said drive current exceeds said suitable threshold value for each said prescribed operation cycle, and to determine presence of abnormality in said drive current when detecting that the maximum value of said drive current exceeds said suitable threshold value in each of said n consecutive prescribed operation cycles.