A tape cartridge which contains a tape-shaped printing medium and is to be mounted on a mounting section of a tape printer includes a tape roll around which the printing medium is wound and a core shaft portion that rotatably supports the tape roll. An inner circumferential portion of the core shaft includes a shape forming a first fitting portion which is fitted to a pedestal portion erectly disposed on the mounting section when the tape cartridge is mounted on the mounting section, and a second fitting portion which is fitted to a first convex portion erectly disposed on the pedestal portion when the tape cartridge is mounted on the mounting section.