A power converter for a railway rolling stock comprising: a plurality of semiconductor devices constituting a power converter circuit; a plurality of gate control circuits for supplying gate signals to the semiconductor devices; a filter capacitor connected to DC terminals of the power converter circuit for smoothing a DC current; a cooling block attached to the semiconductor devices; and a cooling fin for radiating heat generated by the semiconductor devices to the atmosphere; wherein: the semiconductor devices, the filter capacitor, the cooling block, the cooling fin and the gate control circuits are comprised in a power converter unit which is stored within a common box mounted below a floor of the railway rolling stock; characterized in that: the filter capacitor, the semiconductor devices, the cooling block, the cooling fin and the gate control circuits are fixed to each other and fixed and supported to the common box, so that the power converter unit can be attached to and detached from the common box as an integral device; the plurality of gate control circuits are arranged in a space at a front side of the power converter unit and below the filter capacitor; the cooling fin is arranged on the back side of the power converter unit; the plurality of gate control circuits are fixed to a common frame so that the gate control circuits can be attached and detached in a collective manner; wiring between the plurality of gate control circuits and the cooling block adopts a slot-in arrangement, so that the wiring is connected by pushing the common frame into a fixing position with respect to the cooling block; and the plurality of gate control circuits have connecting terminals for receiving input of signals from the exterior at the front side of the gate control circuits. a plurality of semiconductor devices constituting a power converter circuit; a plurality of gate control circuits for supplying gate signals to the semiconductor devices; a filter capacitor connected to DC terminals of the power converter circuit for smoothing a DC current; a cooling block attached to the semiconductor devices; and a cooling fin for radiating heat generated by the semiconductor devices to the atmosphere; the semiconductor devices, the filter capacitor, the cooling block, the cooling fin and the gate control circuits are comprised in a power converter unit which is stored within a common box mounted below a floor of the railway rolling stock; characterized in that: the filter capacitor, the semiconductor devices, the cooling block, the cooling fin and the gate control circuits are fixed to each other and fixed and supported to the common box, so that the power converter unit can be attached to and detached from the common box as an integral device; the plurality of gate control circuits are arranged in a space at a front side of the power converter unit and below the filter capacitor; the cooling fin is arranged on the back side of the power converter unit; the plurality of gate control circuits are fixed to a common frame so that the gate control circuits can be attached and detached in a collective manner; wiring between the plurality of gate control circuits and the cooling block adopts a slot-in arrangement, so that the wiring is connected by pushing the common frame into a fixing position with respect to the cooling block; and the plurality of gate control circuits have connecting terminals for receiving input of signals from the exterior at the front side of the gate control circuits. the filter capacitor, the semiconductor devices, the cooling block, the cooling fin and the gate control circuits are fixed to each other and fixed and supported to the common box, so that the power converter unit can be attached to and detached from the common box as an integral device; the plurality of gate control circuits are arranged in a space at a front side of the power converter unit and below the filter capacitor; the cooling fin is arranged on the back side of the power converter unit; the plurality of gate control circuits are fixed to a common frame so that the gate control circuits can be attached and detached in a collective manner; wiring between the plurality of gate control circuits and the cooling block adopts a slot-in arrangement, so that the wiring is connected by pushing the common frame into a fixing position with respect to the cooling block; and the plurality of gate control circuits have connecting terminals for receiving input of signals from the exterior at the front side of the gate control circuits.