An optical element module (50; 60, 60B, 60C; 70, 70B, 70C, 70D; 80) comprising: an optical element (2; 2A) having a light receiving unit configured to input an optical signal or a light emitting unit configured to output an optical signal; a board (1; 1A, 1B, 1D; 1E) on which the optical element is mounted; and a guide holding member (3; 3A, 3B, 3C; 3E) that has a through hole into which an optical fiber including a core and a cladding is configured to be inserted for inputting and outputting the optical signal to or from the light receiving unit or the light emitting unit of the optical element, and is mounted and arranged to be aligned with the optical element in a thickness direction of the board; wherein: the through hole has a cylindrical shape and has substantially the same diameter as an outer diameter of the optical fiber; a diameter of the light receiving unit or the light emitting unit is smaller than that of the core of the optical fiber, and the optical fiber is a multimode fiber; and an end portion of the through hole that abuts on the board has a tapered shape;and the optical element is flip-chip mounted on the board (1; 1A, 1B, 1D) such that the light emitting unit or the light receiving unit thereof is mounted on the board so as to face to the board, characterized in that: the guide holding member (3; 3A, 3B, 3C; 3E) is mounted on an adhesive on the board, the adhesive being hardened; the guide holding member (3; 3A, 3B, 3C) is mounted on a surface of the board opposite to where the optical element is mounted; and the board has a hole for transmitting and receiving the optical signal between the optical element and the optical fiber positioned on different surfaces. an optical element (2; 2A) having a light receiving unit configured to input an optical signal or a light emitting unit configured to output an optical signal; a board (1; 1A, 1B, 1D; 1E) on which the optical element is mounted; and a guide holding member (3; 3A, 3B, 3C; 3E) that has a through hole into which an optical fiber including a core and a cladding is configured to be inserted for inputting and outputting the optical signal to or from the light receiving unit or the light emitting unit of the optical element, and is mounted and arranged to be aligned with the optical element in a thickness direction of the board; wherein: the through hole has a cylindrical shape and has substantially the same diameter as an outer diameter of the optical fiber; a diameter of the light receiving unit or the light emitting unit is smaller than that of the core of the optical fiber, and the optical fiber is a multimode fiber; and an end portion of the through hole that abuts on the board has a tapered shape;and the through hole has a cylindrical shape and has substantially the same diameter as an outer diameter of the optical fiber; a diameter of the light receiving unit or the light emitting unit is smaller than that of the core of the optical fiber, and the optical fiber is a multimode fiber; and an end portion of the through hole that abuts on the board has a tapered shape;and the optical element is flip-chip mounted on the board (1; 1A, 1B, 1D) such that the light emitting unit or the light receiving unit thereof is mounted on the board so as to face to the board, characterized in that: the guide holding member (3; 3A, 3B, 3C; 3E) is mounted on an adhesive on the board, the adhesive being hardened; the guide holding member (3; 3A, 3B, 3C) is mounted on a surface of the board opposite to where the optical element is mounted; and the board has a hole for transmitting and receiving the optical signal between the optical element and the optical fiber positioned on different surfaces. the guide holding member (3; 3A, 3B, 3C; 3E) is mounted on an adhesive on the board, the adhesive being hardened; the guide holding member (3; 3A, 3B, 3C) is mounted on a surface of the board opposite to where the optical element is mounted; and the board has a hole for transmitting and receiving the optical signal between the optical element and the optical fiber positioned on different surfaces.