There is to provide a power conversion device capable of estimating a junction temperature of a power transistor at a high accuracy. The control device includes a temperature estimation unit and controls the on and off of the power transistor through a driver. The voltage detection circuit detects the inter-terminal voltage of a source and drain terminals during the on-period of the power transistor. The temperature estimation unit previously holds the correlation information between the inter-terminal voltage and inter-terminal current of the source and drain terminals and the junction temperature, and estimates the junction temperature, based on the inter-terminal voltage detected by the voltage detection circuit, the known inter-terminal current, and the correlation information.