A power conversion device, comprising: a power conversion section which can alternately convert between direct current power and alternating current power by turning on and off a plurality of bridge-connected semiconductor switching elements to each of which a free wheel diode is connected in reverse parallel; and a rotating electric machine connected to the alternating current terminals of the power conversion section, wherein the rotating electric machine is a permanent magnet synchronous motor or a permanent magnet synchronous generator driven by a drive source and wherein the power conversion section is an inverter section, wherein the power conversion device is configured to carry out an operation of boosting a direct current voltage of the power conversion section to equal to or more than a specified value by simultaneously and intermittently turning on and off (i) all upper-arm switching elements (41, 42, 43) of the plurality of bridge-connected semiconductor switching elements of the power conversion section which are connected to a positive side direct current terminal of the power conversion section, or (ii) all lower-arm switching elements (44, 45, 46) of the plurality of bridge-connected semiconductor switching elements of the power conversion section which are connected to a negative side direct current terminal of the power conversion section, and wherein the power conversion device is configured to determine whether or not a time measured by an internal timer indicates that a first specified time (T 1) has elapsed from when starting the rotating electric machine, if the specified time (T 1) has elapsed, it is presumed that the direct current intermediate voltage has reached equal to or more than the specified value by the operation of boosting of the power converter section in the specified time (T 1); characterized in that the power conversion device is configured to, when the direct current voltage of the power conversion section is below the specified value when the rotating electric machine is being started, the specified value being a value equal to or greater than an induced voltage between terminals of the rotating electric machine, execute an operation of detecting the speed of the rotating electric machine in a condition in which the direct current voltage of the power conversion section is boosted to equal to or more than the specified value by intermittently turning on and off at least one of the plurality of bridge-connected semiconductor switching elements. a power conversion section which can alternately convert between direct current power and alternating current power by turning on and off a plurality of bridge-connected semiconductor switching elements to each of which a free wheel diode is connected in reverse parallel; and a rotating electric machine connected to the alternating current terminals of the power conversion section, wherein the rotating electric machine is a permanent magnet synchronous motor or a permanent magnet synchronous generator driven by a drive source and wherein the power conversion section is an inverter section, wherein the power conversion device is configured to carry out an operation of boosting a direct current voltage of the power conversion section to equal to or more than a specified value by simultaneously and intermittently turning on and off (i) all upper-arm switching elements (41, 42, 43) of the plurality of bridge-connected semiconductor switching elements of the power conversion section which are connected to a positive side direct current terminal of the power conversion section, or (ii) all lower-arm switching elements (44, 45, 46) of the plurality of bridge-connected semiconductor switching elements of the power conversion section which are connected to a negative side direct current terminal of the power conversion section, and (i) all upper-arm switching elements (41, 42, 43) of the plurality of bridge-connected semiconductor switching elements of the power conversion section which are connected to a positive side direct current terminal of the power conversion section, or (ii) all lower-arm switching elements (44, 45, 46) of the plurality of bridge-connected semiconductor switching elements of the power conversion section which are connected to a negative side direct current terminal of the power conversion section, and wherein the power conversion device is configured to determine whether or not a time measured by an internal timer indicates that a first specified time (T 1) has elapsed from when starting the rotating electric machine, if the specified time (T 1) has elapsed, it is presumed that the direct current intermediate voltage has reached equal to or more than the specified value by the operation of boosting of the power converter section in the specified time (T 1); characterized in that the power conversion device is configured to, when the direct current voltage of the power conversion section is below the specified value when the rotating electric machine is being started, the specified value being a value equal to or greater than an induced voltage between terminals of the rotating electric machine, execute an operation of detecting the speed of the rotating electric machine in a condition in which the direct current voltage of the power conversion section is boosted to equal to or more than the specified value by intermittently turning on and off at least one of the plurality of bridge-connected semiconductor switching elements.