A multipipe heat exchanger used for extracorporeal circulation of blood, comprising: a heat exchanger case; a bottom member attached to one end of said heat exchanger case; and a plurality of heat transfer pipes loaded in inside of said heat exchanger case, in which said blood flows from one end through said bottom member, said bottom member having an annular wall fitted in a fluid-tight manner to said one end of said heat exchanger case, a bottom surface opposed to said one end of said plurality of heat transfer pipes and closing in a fluid-tight manner, an end portion opposite to a side of said annular wall fitted to said heat exchanger case, and a blood inlet port formed like a pipe, having an inside communicating with a space surrounded by said one end of said heat exchanger case, said annular wall, and said bottom surface, and characterized by the blood inlet port extending in a direction of normal to an outer circumferential surface of said annular wall, said bottom surface including a groove portion extending along said direction of normal and a raised bottom portion (96a, 96b) provided on each of opposing end sides of said groove portion, and said raised bottom portion (96a, 96b) being inclined such that a distance between said raised bottom portion (96a, 96b) on a side where said blood inlet port is provided and said one end of said plurality of heat transfer pipes is smaller than a distance between said raised bottom portion (96a, 96b) opposite to the side where said blood inlet port is provided and said one end of said plurality of heat transfer pipes. a heat exchanger case; a bottom member attached to one end of said heat exchanger case; and a plurality of heat transfer pipes loaded in inside of said heat exchanger case, in which said blood flows from one end through said bottom member, said bottom member having an annular wall fitted in a fluid-tight manner to said one end of said heat exchanger case, a bottom surface opposed to said one end of said plurality of heat transfer pipes and closing in a fluid-tight manner, an end portion opposite to a side of said annular wall fitted to said heat exchanger case, and a blood inlet port formed like a pipe, having an inside communicating with a space surrounded by said one end of said heat exchanger case, said annular wall, and said bottom surface, and an annular wall fitted in a fluid-tight manner to said one end of said heat exchanger case, a bottom surface opposed to said one end of said plurality of heat transfer pipes and closing in a fluid-tight manner, an end portion opposite to a side of said annular wall fitted to said heat exchanger case, and a blood inlet port formed like a pipe, having an inside communicating with a space surrounded by said one end of said heat exchanger case, said annular wall, and said bottom surface, and characterized by the blood inlet port extending in a direction of normal to an outer circumferential surface of said annular wall, said bottom surface including a groove portion extending along said direction of normal and a raised bottom portion (96a, 96b) provided on each of opposing end sides of said groove portion, and said raised bottom portion (96a, 96b) being inclined such that a distance between said raised bottom portion (96a, 96b) on a side where said blood inlet port is provided and said one end of said plurality of heat transfer pipes is smaller than a distance between said raised bottom portion (96a, 96b) opposite to the side where said blood inlet port is provided and said one end of said plurality of heat transfer pipes.