An electric power converter including a semiconductor module for converting a DC voltage to an AC voltage and a capacitor device, said semiconductor module comprising a three phase bridge circuit, wherein each bridge circuit comprises an electric circuit device each having an upper arm and a lower arm, each arm being provided with a switching semiconductor element; wherein each of said electric circuit devices comprises: a plate-shaped positive-polarity electrode (130 - 135) comprising a positive side lead terminal portion which constitutes a connection portion of a high-potential input end of said upper arm; and a plate-shaped negative-polarity electrode (140 - 145) comprising a negative side lead terminal portion which constitutes a connection portion of a low-potential input end of said lower arm; wherein said positive side lead terminal portion is arranged so that a main face thereof is opposed to a main face of said negative side lead terminal portion through a clearance; said capacitor device is adapted to suppress changes in DC voltage due to switching operation of the switching semiconductor elements and comprises a capacitor block, a positive polarity capacitor terminal (181, 261) and a negative polarity capacitor terminal (182, 262); wherein said positive side capacitor terminal (181, 261) is arranged so that a main face thereof is opposed to a main face of said negative side capacitor terminal (182, 262), and an insulating sheet (184, 264) being provided between them; wherein said positive polarity capacitor terminal (181, 261) is formed so that a portion thereof protrudes along a protruding direction of a portion of said negative polarity capacitor terminal (182, 262), and is connected electrically to said positive side lead terminal portion; and wherein the negative polarity capacitor terminal (182, 262) is connected electrically to said negative side lead terminal portion, characterised in that said power converter comprises a heat release base comprising insertion sections into which said electric circuit devices are inserted, each insertion section comprising side walls, wherein the heat release base is provided with two flow channels for cooling medium, each of said electric circuit devices has a rectangular parallelepiped body and comprises a first principal heat-releasing surface and a second principal heat-releasing surface arranged to be in thermal contact with the side walls; said plate-shaped positive-polarity electrode (130 - 135) and plate-shaped negative-polarity electrode (140 - 145) comprises a heat-releasing plane (131, 141) which is exposed on the same first or second principal heat releasing surface of the electric circuit device such that heat from the principal planes of each electric circuit device is transferred to the corresponding side wall and then further transferred from the side wall to the coolant medium flowing in the flow channels. a plate-shaped positive-polarity electrode (130 - 135) comprising a positive side lead terminal portion which constitutes a connection portion of a high-potential input end of said upper arm; and a plate-shaped negative-polarity electrode (140 - 145) comprising a negative side lead terminal portion which constitutes a connection portion of a low-potential input end of said lower arm; wherein said positive side lead terminal portion is arranged so that a main face thereof is opposed to a main face of said negative side lead terminal portion through a clearance; said capacitor device is adapted to suppress changes in DC voltage due to switching operation of the switching semiconductor elements and comprises a capacitor block, a positive polarity capacitor terminal (181, 261) and a negative polarity capacitor terminal (182, 262); wherein said positive side capacitor terminal (181, 261) is arranged so that a main face thereof is opposed to a main face of said negative side capacitor terminal (182, 262), and an insulating sheet (184, 264) being provided between them; wherein said positive polarity capacitor terminal (181, 261) is formed so that a portion thereof protrudes along a protruding direction of a portion of said negative polarity capacitor terminal (182, 262), and is connected electrically to said positive side lead terminal portion; and wherein the negative polarity capacitor terminal (182, 262) is connected electrically to said negative side lead terminal portion, characterised in that said power converter comprises a heat release base comprising insertion sections into which said electric circuit devices are inserted, each insertion section comprising side walls, wherein the heat release base is provided with two flow channels for cooling medium, each of said electric circuit devices has a rectangular parallelepiped body and comprises a first principal heat-releasing surface and a second principal heat-releasing surface arranged to be in thermal contact with the side walls; said plate-shaped positive-polarity electrode (130 - 135) and plate-shaped negative-polarity electrode (140 - 145) comprises a heat-releasing plane (131, 141) which is exposed on the same first or second principal heat releasing surface of the electric circuit device such that heat from the principal planes of each electric circuit device is transferred to the corresponding side wall and then further transferred from the side wall to the coolant medium flowing in the flow channels.