A liquid supplying unit configured to be inserted into a mounting unit of a printing device in an insertion direction, the liquid supplying unit comprising: a casing defining therein a storage chamber configured to store liquid, the casing having a first casing surface and a second casing surface perpendicular to each other; a liquid outlet portion provided at the first casing surface and configured to supply the liquid in the storage chamber to outside; and a circuit substrate fixed to the second casing surface and comprising: a substrate body having a rectangular shape configured of four sides, the four sides including a first side and a second side extending in a first direction coincident with the insertion direction and opposing each other in a second direction orthogonal to the first direction, the substrate body having a top surface; and an electrode mounted on the top surface of the substrate body, the electrode having a first outer point positioned closest to the first side in the second direction and a second outer point positioned closest to the second side in the second direction, a first imaginary line being defined as a line extending in the first direction and passing through the first outer point, and a second imaginary line being defined as a line extending in the first direction and passing through the second outer point, wherein the top surface has: a first area defined between the first side and the first imaginary line; a second area defined between the second side and the second imaginary line; and a third area interposed between the first area and the second area in the second direction, characterized in that the substrate body is formed with a first opening (21, 22) in the first area at a position closer to the first casing surface than the electrode is to the first casing surface in the first direction, and wherein the second casing surface is formed with a first protrusion (31, 32) at a position corresponding to the first opening (21, 22). a casing defining therein a storage chamber configured to store liquid, the casing having a first casing surface and a second casing surface perpendicular to each other; a liquid outlet portion provided at the first casing surface and configured to supply the liquid in the storage chamber to outside; and a circuit substrate fixed to the second casing surface and comprising: a substrate body having a rectangular shape configured of four sides, the four sides including a first side and a second side extending in a first direction coincident with the insertion direction and opposing each other in a second direction orthogonal to the first direction, the substrate body having a top surface; and an electrode mounted on the top surface of the substrate body, the electrode having a first outer point positioned closest to the first side in the second direction and a second outer point positioned closest to the second side in the second direction, a first imaginary line being defined as a line extending in the first direction and passing through the first outer point, and a second imaginary line being defined as a line extending in the first direction and passing through the second outer point, a substrate body having a rectangular shape configured of four sides, the four sides including a first side and a second side extending in a first direction coincident with the insertion direction and opposing each other in a second direction orthogonal to the first direction, the substrate body having a top surface; and an electrode mounted on the top surface of the substrate body, the electrode having a first outer point positioned closest to the first side in the second direction and a second outer point positioned closest to the second side in the second direction, a first imaginary line being defined as a line extending in the first direction and passing through the first outer point, and a second imaginary line being defined as a line extending in the first direction and passing through the second outer point, wherein the top surface has: a first area defined between the first side and the first imaginary line; a second area defined between the second side and the second imaginary line; and a third area interposed between the first area and the second area in the second direction, characterized in that the substrate body is formed with a first opening (21, 22) in the first area at a position closer to the first casing surface than the electrode is to the first casing surface in the first direction, and a first area defined between the first side and the first imaginary line; a second area defined between the second side and the second imaginary line; and a third area interposed between the first area and the second area in the second direction, characterized in that the substrate body is formed with a first opening (21, 22) in the first area at a position closer to the first casing surface than the electrode is to the first casing surface in the first direction, and wherein the second casing surface is formed with a first protrusion (31, 32) at a position corresponding to the first opening (21, 22).