An abnormality detection apparatus for an electrically heated catalyst comprising: an electrically heated catalyst provided in an exhaust passage of an internal combustion engine, including an exhaust gas purification catalyst and a heating element that generates heat when supplied with electrical power, the electrical resistance of the heating element being larger when its temperature is low than when it is high; an electrical power supply unit configured to adjust an applied voltage defined as a voltage applied to the electrically heated catalyst in such a way as to make the electrical power as the product of the applied voltage and a catalyst current defined as the electrical current flowing through the electrically heated catalyst per unit time equal to a target electrical power to be supplied to the electrically heated catalyst and to adjust the applied voltage to a voltage substantially equal to a specific upper limit voltage, wherein the specific upper limit voltage is a design upper limit voltage determined by the structure and performance of the electrical power supply unit supplying power to the electrically heated catalyst, when the electrical power that can be supplied to the electrically heated catalyst by applying a voltage equal to or lower than the specific upper limit voltage is lower than the target electrical power; a first calculation unit configured to calculate an actually supplied electrical energy defined as the integrated value of the electrical power actually supplied to the electrically heated catalyst over a specific period from the time when the application of the applied voltage to the electrically heated catalyst by the electrical power supply unit is started; a second calculation unit configured to calculate a target electrical energy defined as the integrated value of the target electrical power over the specific period; a third calculation unit configured to calculate an accomplishment ratio parameter relating to the ratio of the actually supplied electrical energy calculated by the first calculation unit to the target electrical energy calculated by the second calculation unit; a detection unit configured to detect an abnormality of the electrically heated catalyst by comparing the accomplishment ratio parameter calculated by the third calculation unit and a specific threshold; an acquisition unit configured to acquire a temperature parameter relating to the temperature of the electrically heated catalyst at the time when the supply of electrical power is started; and a setting unit configured to set the specific threshold according to the temperature parameter acquired by the acquisition unit. an electrically heated catalyst provided in an exhaust passage of an internal combustion engine, including an exhaust gas purification catalyst and a heating element that generates heat when supplied with electrical power, the electrical resistance of the heating element being larger when its temperature is low than when it is high; an electrical power supply unit configured to adjust an applied voltage defined as a voltage applied to the electrically heated catalyst in such a way as to make the electrical power as the product of the applied voltage and a catalyst current defined as the electrical current flowing through the electrically heated catalyst per unit time equal to a target electrical power to be supplied to the electrically heated catalyst and to adjust the applied voltage to a voltage substantially equal to a specific upper limit voltage, wherein the specific upper limit voltage is a design upper limit voltage determined by the structure and performance of the electrical power supply unit supplying power to the electrically heated catalyst, when the electrical power that can be supplied to the electrically heated catalyst by applying a voltage equal to or lower than the specific upper limit voltage is lower than the target electrical power; a first calculation unit configured to calculate an actually supplied electrical energy defined as the integrated value of the electrical power actually supplied to the electrically heated catalyst over a specific period from the time when the application of the applied voltage to the electrically heated catalyst by the electrical power supply unit is started; a second calculation unit configured to calculate a target electrical energy defined as the integrated value of the target electrical power over the specific period; a third calculation unit configured to calculate an accomplishment ratio parameter relating to the ratio of the actually supplied electrical energy calculated by the first calculation unit to the target electrical energy calculated by the second calculation unit; a detection unit configured to detect an abnormality of the electrically heated catalyst by comparing the accomplishment ratio parameter calculated by the third calculation unit and a specific threshold; an acquisition unit configured to acquire a temperature parameter relating to the temperature of the electrically heated catalyst at the time when the supply of electrical power is started; and a setting unit configured to set the specific threshold according to the temperature parameter acquired by the acquisition unit.