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 (S) 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 provided on each of opposing end sides of said groove portion , and said raised bottom portion being inclined such that a distance (H2) between said raised bottom portion 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 (H1) between said raised bottom portion 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 (S) 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 (S) 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 provided on each of opposing end sides of said groove portion , and said raised bottom portion being inclined such that a distance (H2) between said raised bottom portion 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 (H1) between said raised bottom portion opposite to the side where said blood inlet port is provided and said one end of said plurality of heat transfer pipes . <EOS>