A cooling structure of an electric rotating machine comprising: a water jacket having a cylindrical shape and internally including a jacket channel configured to allow passage of a coolant; a stator disposed on an inner circumference of the water jacket, the stator having a circular shape; a winding wire wound on the stator; a thermal conductor integrated with an inner circumferential surface of the water jacket, the thermal conductor (15, 37) being formed of resin having a high thermal conductivity and molded to cover the winding wire and the stator in mold forming; and wherein the jacket channel is formed to have a zigzag shape extending in a circumferential direction of the water jacket within a width of the water jacket, the width extending between both ends of the water jacket in an axial direction of the water jacket, the jacket channel includes a plurality of straight holes (al) extending along the axial direction and formed by being bored parallel in the circumferential direction; first communication groove communicating with one ends of the straight holes (al) adjacent to each other; and a second communication groove communicating with the other end of one of the straight holes (al) and with the other end of the other one of the other straight holes (al) adjacent to the one of the straight hole, characterized by a motor housing separated from the water jacket, wherein the water jacket is formed of material having a high thermal conductivity and disposed in the motor housing, the thermal conductor (15, 37) has a width on an inner side of a diameter of the stator and another width on an outer side of the diameter of the stator, the another width being wider than the width, the width and the another width extending in an axial direction of the stator, the thermal conductor (15, 37) includes a portion on the outer side of the diameter of the stator, the portion having a width substantially corresponding to a full width of the water jacket in the axial direction of the water jacket, the thermal conductor (15, 37) has tapered side surfaces at both side in the axial direction of the stator, and wherein the first and second communication grooves (a2, a3) are closed by seal rings arranged on both ends of the water jacket in the axial direction, and a coolant channel (18, 38) is formed inside the thermal conductor (15, 37). a water jacket having a cylindrical shape and internally including a jacket channel configured to allow passage of a coolant; a stator disposed on an inner circumference of the water jacket, the stator having a circular shape; a winding wire wound on the stator; a thermal conductor integrated with an inner circumferential surface of the water jacket, the thermal conductor (15, 37) being formed of resin having a high thermal conductivity and molded to cover the winding wire and the stator in mold forming; and wherein the jacket channel is formed to have a zigzag shape extending in a circumferential direction of the water jacket within a width of the water jacket, the width extending between both ends of the water jacket in an axial direction of the water jacket, the jacket channel includes a plurality of straight holes (al) extending along the axial direction and formed by being bored parallel in the circumferential direction; first communication groove communicating with one ends of the straight holes (al) adjacent to each other; and a second communication groove communicating with the other end of one of the straight holes (al) and with the other end of the other one of the other straight holes (al) adjacent to the one of the straight hole, characterized by a motor housing separated from the water jacket, first communication groove communicating with one ends of the straight holes (al) adjacent to each other; and a second communication groove communicating with the other end of one of the straight holes (al) and with the other end of the other one of the other straight holes (al) adjacent to the one of the straight hole, characterized by a motor housing separated from the water jacket, wherein the water jacket is formed of material having a high thermal conductivity and disposed in the motor housing, the thermal conductor (15, 37) has a width on an inner side of a diameter of the stator and another width on an outer side of the diameter of the stator, the another width being wider than the width, the width and the another width extending in an axial direction of the stator, the thermal conductor (15, 37) includes a portion on the outer side of the diameter of the stator, the portion having a width substantially corresponding to a full width of the water jacket in the axial direction of the water jacket, the thermal conductor (15, 37) has tapered side surfaces at both side in the axial direction of the stator, and wherein the first and second communication grooves (a2, a3) are closed by seal rings arranged on both ends of the water jacket in the axial direction, and a coolant channel (18, 38) is formed inside the thermal conductor (15, 37).