A power conversion apparatus (10, 10A) comprising: a power conversion unit; a plurality of sensors attached to the power conversion unit; and a control unit (14, 14A) configured to control the power conversion unit, wherein the power conversion unit includes a module having a power semiconductor device to perform a power conversion and a metal base on which the power semiconductor device is mounted, and a heat sink arranged to contact the metal base to cool the power semiconductor device, wherein the plurality of sensors includes a first temperature sensor configured to measure a temperature of the metal base, wherein the first temperature sensor is inserted in a recess formed in the metal base or disposed so as to be in contact with the metal base, wherein the plurality of sensors further includes second temperature sensors (26b, 26c) arranged to measure a temperature of cooling water flowing into and out of the heat sink, and a flow rate sensor arranged to measure a flow rate of cooling water, wherein the control unit (14, 14A) is configured to estimate an initial junction temperature of the power semiconductor device based on the temperature of the metal base and a quantity of heat that flows from the power semiconductor device to the heat sink, wherein the quantity of heat is determined by the temperatures measured by the second temperature sensors (26b, 26c) and the flow rate detected by the flow rate sensor, wherein the control unit (14, 14A) is configured to further estimate, upon receipt of an output change instruction to increase power to be output from the power conversion unit, an updated junction temperature of the power semiconductor device based on increased power in accordance with the output change instruction and on the estimated initial junction temperature of the power semiconductor device, and wherein the control unit (14, 14A) is configured to become non-responsive to the output change instruction when the control unit (14, 14A) determines that the updated junction temperature reaches a given temperature. a power conversion unit; a plurality of sensors attached to the power conversion unit; and a control unit (14, 14A) configured to control the power conversion unit, wherein the power conversion unit includes a module having a power semiconductor device to perform a power conversion and a metal base on which the power semiconductor device is mounted, and a heat sink arranged to contact the metal base to cool the power semiconductor device, wherein the plurality of sensors includes a first temperature sensor configured to measure a temperature of the metal base, wherein the first temperature sensor is inserted in a recess formed in the metal base or disposed so as to be in contact with the metal base, wherein the plurality of sensors further includes second temperature sensors (26b, 26c) arranged to measure a temperature of cooling water flowing into and out of the heat sink, and a flow rate sensor arranged to measure a flow rate of cooling water, wherein the control unit (14, 14A) is configured to estimate an initial junction temperature of the power semiconductor device based on the temperature of the metal base and a quantity of heat that flows from the power semiconductor device to the heat sink, wherein the quantity of heat is determined by the temperatures measured by the second temperature sensors (26b, 26c) and the flow rate detected by the flow rate sensor, wherein the control unit (14, 14A) is configured to further estimate, upon receipt of an output change instruction to increase power to be output from the power conversion unit, an updated junction temperature of the power semiconductor device based on increased power in accordance with the output change instruction and on the estimated initial junction temperature of the power semiconductor device, and wherein the control unit (14, 14A) is configured to become non-responsive to the output change instruction when the control unit (14, 14A) determines that the updated junction temperature reaches a given temperature.