An information reading device (1a to 1f) comprising: a base module ; and three functional modules (20a, 20b, 20c; 30a, 30d; 40a, 40c, 40e), which are a top module , a bottom module , and a back module , at least the top module and the bottom module being configured to be detachably connected to the base module to impart a predetermined function, wherein the base module includes a control unit that performs control by using the three functional modules (20a, 20b, 20c; 30a, 30d; 40a, 40c, 40e), and a display unit whose display content is controlled by the control unit , the top module is detachably connected to a one end of the base module in a longitudinal direction of the base module , and includes a casing and a first reading unit for optically reading an information code positioned outside the device and a sound unit , the first reading unit and the sound unit are housed in the outer casing, the bottom module is detachably connected to an other end of the base module in the longitudinal direction of the base module , and includes a casing in which at least one of a second reading unit for reading external information, a key operation unit , and a battery unit is housed, the back module is connected to a rear side of the base module , which faces away from a display screen of the display unit , and includes a casing in which at least one of a third reading unit (26c etc.) for reading external information, an antenna , a charging unit , and a grip is housed, and the control unit recognizes each function on a basis of information obtained from the three functional modules connected to the base module . a base module ; and three functional modules (20a, 20b, 20c; 30a, 30d; 40a, 40c, 40e), which are a top module , a bottom module , and a back module , at least the top module and the bottom module being configured to be detachably connected to the base module to impart a predetermined function, wherein the base module includes a control unit that performs control by using the three functional modules (20a, 20b, 20c; 30a, 30d; 40a, 40c, 40e), and a display unit whose display content is controlled by the control unit , the top module is detachably connected to a one end of the base module in a longitudinal direction of the base module , and includes a casing and a first reading unit for optically reading an information code positioned outside the device and a sound unit , the first reading unit and the sound unit are housed in the outer casing, the bottom module is detachably connected to an other end of the base module in the longitudinal direction of the base module , and includes a casing in which at least one of a second reading unit for reading external information, a key operation unit , and a battery unit is housed, the back module is connected to a rear side of the base module , which faces away from a display screen of the display unit , and includes a casing in which at least one of a third reading unit (26c etc.) for reading external information, an antenna , a charging unit , and a grip is housed, and the control unit recognizes each function on a basis of information obtained from the three functional modules connected to the base module . <EOS>