A liquid-cooling-type cooler comprising: a heat sink having a first heat dissipation fin; a jacket having a second heat dissipation fin and forming a cooling container together with the heat sink; and a partition member (4, 4A, 4B, 4C, 4D) disposed between the first heat dissipation fin and the second heat dissipation fin which are disposed so as to face each other in the cooling container, wherein the cooling container separately has, in a pair of side wall surfaces (1c, 1d) thereof facing each other, an inflow port and an outflow port for a coolant and has an inlet flow path (7, 7a, 7b) and an outlet flow path (8, 8a, 8b) which are disposed parallel to each other along another pair of side wall surfaces (1a, 1b), of the cooling container, that face each other, the partition member (4, 4A, 4B, 4C, 4D) has a pair of sheet portions (41, 41A, 41B, 42, 42A, 42B) which are respectively in contact with the first heat dissipation fin and the second heat dissipation fin, and a partition wall (43, 43a, 43b, 43A, 43B, 43C, 43D, 44) coupling the pair of sheet portions (41, 41A, 41B, 42, 42A, 42B), two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d) are formed by one of the sheet portions (41, 41A, 41B) and the first heat dissipation fin, and the other sheet portion (42, 42A, 42B) and the second heat dissipation fin, respectively, an inlet header region (6, 6a, 6b) and an outlet header region (9, 9a, 9b) are formed, between the two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d), by the pair of sheet portions (41, 41A, 41B, 42, 42A, 42B) and the partition wall (43, 43a, 43b, 43A, 43B, 43C, 43D, 44), the inlet header region (6, 6a, 6b) communicates with the inflow port, the outlet header region (9, 9a, 9b) communicates with the outflow port, and the two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d) communicate with the inlet header region (6, 6a, 6b) via the inlet flow path (7, 7a, 7b) and communicate with the outlet header region (9, 9a, 9b) via the outlet flow path (8, 8a, 8b), and if, in a plane parallel to a mounting surface for the first heat dissipation fin, an inflow direction of a coolant to the inflow port is defined as a Y direction and a direction perpendicular to the Y direction is defined as an X direction, the partition member (4, 4A, 4B, 4C, 4D) guides a coolant, which has flowed in the Y direction into the inlet header region (6, 6a, 6b), to the inlet flow path (7, 7a, 7b) while deflecting an advancing direction of the coolant by the partition wall (43, 43a, 43b, 43A, 43B, 43C, 43D, 44), and causes the coolant to flow in the X direction from the inlet flow path (7, 7a, 7b) into the two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d). a heat sink having a first heat dissipation fin; a jacket having a second heat dissipation fin and forming a cooling container together with the heat sink; and a partition member (4, 4A, 4B, 4C, 4D) disposed between the first heat dissipation fin and the second heat dissipation fin which are disposed so as to face each other in the cooling container, wherein the cooling container separately has, in a pair of side wall surfaces (1c, 1d) thereof facing each other, an inflow port and an outflow port for a coolant and has an inlet flow path (7, 7a, 7b) and an outlet flow path (8, 8a, 8b) which are disposed parallel to each other along another pair of side wall surfaces (1a, 1b), of the cooling container, that face each other, the partition member (4, 4A, 4B, 4C, 4D) has a pair of sheet portions (41, 41A, 41B, 42, 42A, 42B) which are respectively in contact with the first heat dissipation fin and the second heat dissipation fin, and a partition wall (43, 43a, 43b, 43A, 43B, 43C, 43D, 44) coupling the pair of sheet portions (41, 41A, 41B, 42, 42A, 42B), a pair of sheet portions (41, 41A, 41B, 42, 42A, 42B) which are respectively in contact with the first heat dissipation fin and the second heat dissipation fin, and a partition wall (43, 43a, 43b, 43A, 43B, 43C, 43D, 44) coupling the pair of sheet portions (41, 41A, 41B, 42, 42A, 42B), two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d) are formed by one of the sheet portions (41, 41A, 41B) and the first heat dissipation fin, and the other sheet portion (42, 42A, 42B) and the second heat dissipation fin, respectively, an inlet header region (6, 6a, 6b) and an outlet header region (9, 9a, 9b) are formed, between the two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d), by the pair of sheet portions (41, 41A, 41B, 42, 42A, 42B) and the partition wall (43, 43a, 43b, 43A, 43B, 43C, 43D, 44), the inlet header region (6, 6a, 6b) communicates with the inflow port, the outlet header region (9, 9a, 9b) communicates with the outflow port, and the two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d) communicate with the inlet header region (6, 6a, 6b) via the inlet flow path (7, 7a, 7b) and communicate with the outlet header region (9, 9a, 9b) via the outlet flow path (8, 8a, 8b), and if, in a plane parallel to a mounting surface for the first heat dissipation fin, an inflow direction of a coolant to the inflow port is defined as a Y direction and a direction perpendicular to the Y direction is defined as an X direction, the partition member (4, 4A, 4B, 4C, 4D) guides a coolant, which has flowed in the Y direction into the inlet header region (6, 6a, 6b), to the inlet flow path (7, 7a, 7b) while deflecting an advancing direction of the coolant by the partition wall (43, 43a, 43b, 43A, 43B, 43C, 43D, 44), and causes the coolant to flow in the X direction from the inlet flow path (7, 7a, 7b) into the two layers of heat dissipation regions (11, 11a, 11b, 11c, 11d).