A power conversion apparatus, comprising: a power semiconductor module (300a-300c) that has a power semiconductor element to convert a direct current into an alternating current; a smoothing capacitor module that is configured to smooth the direct current; an alternating-current bus bar (801a-801c) that is configured to transmit an alternating-current output of the power semiconductor element; a control circuit unit that is configured to control the power semiconductor element; and a flow channel formation body that forms a flow channel through which a cooling medium flows, wherein the power semiconductor module (300a-300c) has a first heat dissipation portion and a second heat dissipation portion facing the first heat dissipation portion with the power semiconductor element therebetween, characterized in that a housing houses the power semiconductor module (300a - 300c), the smoothing capacitor module, the alternating-current bus bar (801a-801c) and the control circuit unit which form a power conversion module, the flow channel formation body has a top surface that faces the first heat dissipation portion of the power semiconductor module (300a-300c) with the flow channel therebetween and a bottom surface that faces the second heat dissipation portion of the power semiconductor module (300a-300c) with the flow channel therebetween, at the opposite side of the top surface with the power semiconductor module (300a-300c) therebetween, an opening (402a-402c) to insert the power semiconductor module (300a-300c) into the flow channel is formed on a side of the flow channel formation body, being arranged between the top surface and the bottom surface, the smoothing capacitor module is arranged at a position facing the bottom surface of the flow channel formation body, the alternating-current bus bar (801a-801c) is arranged at a position facing the top surface of the flow channel formation body, and the control circuit unit is arranged at a position facing the alternating-current bus bar (801a-801c), at the opposite side of the top surface of the flow channel formation body with the alternating-current bus bar (801a-801c) therebetween. a power semiconductor module (300a-300c) that has a power semiconductor element to convert a direct current into an alternating current; a smoothing capacitor module that is configured to smooth the direct current; an alternating-current bus bar (801a-801c) that is configured to transmit an alternating-current output of the power semiconductor element; a control circuit unit that is configured to control the power semiconductor element; and a flow channel formation body that forms a flow channel through which a cooling medium flows, wherein the power semiconductor module (300a-300c) has a first heat dissipation portion and a second heat dissipation portion facing the first heat dissipation portion with the power semiconductor element therebetween, characterized in that a housing houses the power semiconductor module (300a - 300c), the smoothing capacitor module, the alternating-current bus bar (801a-801c) and the control circuit unit which form a power conversion module, the flow channel formation body has a top surface that faces the first heat dissipation portion of the power semiconductor module (300a-300c) with the flow channel therebetween and a bottom surface that faces the second heat dissipation portion of the power semiconductor module (300a-300c) with the flow channel therebetween, at the opposite side of the top surface with the power semiconductor module (300a-300c) therebetween, an opening (402a-402c) to insert the power semiconductor module (300a-300c) into the flow channel is formed on a side of the flow channel formation body, being arranged between the top surface and the bottom surface, the smoothing capacitor module is arranged at a position facing the bottom surface of the flow channel formation body, the alternating-current bus bar (801a-801c) is arranged at a position facing the top surface of the flow channel formation body, and the control circuit unit is arranged at a position facing the alternating-current bus bar (801a-801c), at the opposite side of the top surface of the flow channel formation body with the alternating-current bus bar (801a-801c) therebetween.