A liquid cartridge (30, 30A, 30B, 30C, 30D) attachable to a printer in an attached posture by being moved in a front-rear direction (51/52) crossing an up-down direction (53/54) along a gravitational direction, the liquid cartridge comprising: a cartridge case defining a liquid storage chamber (36, 37) therein; a liquid supply portion protruding frontward from a front surface of the cartridge case and configured to supply liquid stored in the liquid storage chamber to an outside of the liquid storage chamber; a circuit board comprising an electrode group comprising at least three electrodes (65A, 65B, 65C), the at least three electrodes (65A, 65B, 65C) facing upward and being exposed to the outside in the attached posture; a plate member (91, 68), the plate member being positioned rearward and upward of the electrode group in the attached posture, the plate member (91, 68) extending in the front-rear direction in the attached posture and having a front end movable in the front-rear direction; and a residual-amount detecting portion configured to change a state of incident light according to an amount of the liquid stored in the liquid storage chamber (36, 37), the residual-amount detecting portion comprising an optical access portion (132A, 132B) accessible by light traveling in a left-right direction (55/56) crossing the up-down direction and the front-rear direction in the attached posture, the optical access portion (132A, 132B) including a portion (133A, 133B) positioned above and away from the electrode group by a first distance, characterized in that the plate member (91, 68) is movable between a first position and a second position, the plate member (91, 68) having a portion positioned frontward of the optical access portion (132A, 132B) and above and away from the electrode group by the first distance when the plate member (91, 68) is at the first position, the front end of the plate member being positioned closer to the residual-amount detecting portion when the plate member is at the second position than when the plate member is at the first position, and wherein the plate member (91, 68) at the first position and the residual-amount detecting portion define a light transmissive region therebetween in the front-rear direction, the light transmissive region having a light transmittance higher than a light transmittance of the plate member (91, 68). a cartridge case defining a liquid storage chamber (36, 37) therein; a liquid supply portion protruding frontward from a front surface of the cartridge case and configured to supply liquid stored in the liquid storage chamber to an outside of the liquid storage chamber; a circuit board comprising an electrode group comprising at least three electrodes (65A, 65B, 65C), the at least three electrodes (65A, 65B, 65C) facing upward and being exposed to the outside in the attached posture; a plate member (91, 68), the plate member being positioned rearward and upward of the electrode group in the attached posture, the plate member (91, 68) extending in the front-rear direction in the attached posture and having a front end movable in the front-rear direction; and a residual-amount detecting portion configured to change a state of incident light according to an amount of the liquid stored in the liquid storage chamber (36, 37), the residual-amount detecting portion comprising an optical access portion (132A, 132B) accessible by light traveling in a left-right direction (55/56) crossing the up-down direction and the front-rear direction in the attached posture, the optical access portion (132A, 132B) including a portion (133A, 133B) positioned above and away from the electrode group by a first distance, characterized in that the plate member (91, 68) is movable between a first position and a second position, the plate member (91, 68) having a portion positioned frontward of the optical access portion (132A, 132B) and above and away from the electrode group by the first distance when the plate member (91, 68) is at the first position, the front end of the plate member being positioned closer to the residual-amount detecting portion when the plate member is at the second position than when the plate member is at the first position, and wherein the plate member (91, 68) at the first position and the residual-amount detecting portion define a light transmissive region therebetween in the front-rear direction, the light transmissive region having a light transmittance higher than a light transmittance of the plate member (91, 68).