A printing-fluid containing device (30, 160) configured with an insertion direction in which to be inserted into a cartridge attachment section so as to be detachably attached to the cartridge attachment section, the printing-fluid containing device (30, 160) comprising: a printing-fluid cartridge comprising: a casing configured to store printing-fluid therein; a supply portion configured to allow the printing-fluid stored in the casing to flow out of the casing; and a detection portion including a light accessible portion (62, 33) configured to be accessed by light emitted from an outside of the printing-fluid cartridge; and an adaptor to which the printing-fluid cartridge is configured to be detachably assembled, the adaptor comprising: an adaptor body into which the printing-fluid cartridge is insertable, the adaptor body having a leading end and a trailing end in the insertion direction, the adaptor body having a front wall at the leading end, the front wall having an opening through which the supply portion extends, the adaptor body further having an outer surface; and an electrical interface disposed on the outer surface and electrically connectable to an electric contact provided at the cartridge attachment section; wherein the casing has a top surface facing in an upward direction that is opposite to a gravitational direction when the printing-fluid cartridge is at an insertion posture that is a posture of the printing-fluid cartridge during a process of the printing-fluid cartridge being inserted into the cartridge attachment section; wherein the adaptor body has an opening formed at the trailing end, the adaptor body further having a top wall facing in the upward direction opposite to the gravitational direction when the adaptor is inserted into the cartridge attachment section, the top wall being positioned between the front wall and the opening formed at the trailing end, and wherein the casing has a leading end and a trailing end in the insertion direction; characterized in that the printing-fluid cartridge further comprises: an engagement portion (171, 94) configured to engage with the cartridge attachment section; wherein the light accessible portion (62, 33) is disposed at a position further upward than the top surface; the light accessible portion (62, 33) being disposed at a position further upward than the top wall of the adaptor body in a state where the printing-fluid cartridge is inserted into the adaptor body; and wherein the light accessible portion (62, 33) is positioned closer to the leading end of the casing than the engagement portion (171, 94) is to the leading end of the casing in the insertion direction in a state where the printing-fluid cartridge is at the insertion posture. a casing configured to store printing-fluid therein; a supply portion configured to allow the printing-fluid stored in the casing to flow out of the casing; and a detection portion including a light accessible portion (62, 33) configured to be accessed by light emitted from an outside of the printing-fluid cartridge; and an adaptor to which the printing-fluid cartridge is configured to be detachably assembled, the adaptor comprising: an adaptor body into which the printing-fluid cartridge is insertable, the adaptor body having a leading end and a trailing end in the insertion direction, the adaptor body having a front wall at the leading end, the front wall having an opening through which the supply portion extends, the adaptor body further having an outer surface; and an electrical interface disposed on the outer surface and electrically connectable to an electric contact provided at the cartridge attachment section; an adaptor body into which the printing-fluid cartridge is insertable, the adaptor body having a leading end and a trailing end in the insertion direction, the adaptor body having a front wall at the leading end, the front wall having an opening through which the supply portion extends, the adaptor body further having an outer surface; and an electrical interface disposed on the outer surface and electrically connectable to an electric contact provided at the cartridge attachment section; wherein the casing has a top surface facing in an upward direction that is opposite to a gravitational direction when the printing-fluid cartridge is at an insertion posture that is a posture of the printing-fluid cartridge during a process of the printing-fluid cartridge being inserted into the cartridge attachment section; wherein the adaptor body has an opening formed at the trailing end, the adaptor body further having a top wall facing in the upward direction opposite to the gravitational direction when the adaptor is inserted into the cartridge attachment section, the top wall being positioned between the front wall and the opening formed at the trailing end, and wherein the casing has a leading end and a trailing end in the insertion direction; characterized in that the printing-fluid cartridge further comprises: an engagement portion (171, 94) configured to engage with the cartridge attachment section; wherein the light accessible portion (62, 33) is disposed at a position further upward than the top surface; the light accessible portion (62, 33) being disposed at a position further upward than the top wall of the adaptor body in a state where the printing-fluid cartridge is inserted into the adaptor body; and wherein the light accessible portion (62, 33) is positioned closer to the leading end of the casing than the engagement portion (171, 94) is to the leading end of the casing in the insertion direction in a state where the printing-fluid cartridge is at the insertion posture.