the ink cartridges 32 a 32 b on the basis of a value detected by the light receiving element 30 b of the optical sensor 30 as shown in fig4 and 6 on the bottom of the cartridge holder 31 two reflectors reflectors for detecting mounting condition 40 a 40 b are fixed in a row along the moving direction of the carriage 18 the moving path l of the optical sensor 30 in an upwardly protruding posture each of the reflectors 40 a 40 b has a prism part 40 a in a shape of a right triangle prism and reflective light paths of the optical sensor 30 are formed by two prism reflective faces s 3 s 4 which are at a right angle with respect to each other in the same manner as the reflectors 39 a 39 b for detecting the amount of the remaining ink on the other hand recesses hollowed parts 41 a 41 b are integrally formed in respective lower portions of the ink cartridges 32 a 328 when the ink cartridges 32 a 32 b have been mounted at the predetermined positions of the cartridge holder 31 the reflectors 40 a 40 b are inserted into the recesses 41 a 41 b and the surroundings are covered on this occasion.