A power supply apparatus comprising: a power supply; a drive circuit receiving electric power from said power supply to drive a load circuit; and an abnormal current detection circuit detecting an abnormality in drive current flowing in said drive circuit, said abnormal current detection circuit detecting that a current integral of said drive current is larger than a predetermined threshold to determine that said drive current is abnormal, wherein said abnormal current detection circuit includes: current detection means for sampling said drive current at every predetermined calculation cycle; current integral calculation means for integrating said sampled drive current over a plurality of said predetermined calculation cycles consumed for the sampling to calculate the current integral of said drive current; and abnormality determination means for determining whether the current integral of said drive current is larger than said predetermined threshold, detecting that the current integral of said drive current is larger than said predetermined threshold and determining that said drive current is abnormal, and wherein said load circuit includes an AC motor, said abnormal current detection circuit includes mode determination means for determining a control mode of said AC motor, said mode determination means determines a control mode of said AC motor when said drive current that is out of a normal operating range flows, and said abnormality determination means adjusts said predetermined threshold to an appropriate threshold that is appropriate for said determined control mode, determines whether the current integral of said drive current is larger than said appropriate threshold, detects that the current integral of said drive current is larger than said appropriate threshold, and determines that said drive current is abnormal. a power supply; a drive circuit receiving electric power from said power supply to drive a load circuit; and an abnormal current detection circuit detecting an abnormality in drive current flowing in said drive circuit, said abnormal current detection circuit detecting that a current integral of said drive current is larger than a predetermined threshold to determine that said drive current is abnormal, wherein said abnormal current detection circuit includes: current detection means for sampling said drive current at every predetermined calculation cycle; current integral calculation means for integrating said sampled drive current over a plurality of said predetermined calculation cycles consumed for the sampling to calculate the current integral of said drive current; and abnormality determination means for determining whether the current integral of said drive current is larger than said predetermined threshold, detecting that the current integral of said drive current is larger than said predetermined threshold and determining that said drive current is abnormal, and wherein current detection means for sampling said drive current at every predetermined calculation cycle; current integral calculation means for integrating said sampled drive current over a plurality of said predetermined calculation cycles consumed for the sampling to calculate the current integral of said drive current; and abnormality determination means for determining whether the current integral of said drive current is larger than said predetermined threshold, detecting that the current integral of said drive current is larger than said predetermined threshold and determining that said drive current is abnormal, and wherein said load circuit includes an AC motor, said abnormal current detection circuit includes mode determination means for determining a control mode of said AC motor, said mode determination means determines a control mode of said AC motor when said drive current that is out of a normal operating range flows, and said abnormality determination means adjusts said predetermined threshold to an appropriate threshold that is appropriate for said determined control mode, determines whether the current integral of said drive current is larger than said appropriate threshold, detects that the current integral of said drive current is larger than said appropriate threshold, and determines that said drive current is abnormal.