A thermal printer configured for preventing fluttering of a sheet during its printing by a thermal head for preventing printing failure or a sheet jam. A thermal head (26) opposes a platen roller (28). A scale (60) is provided in a fixed guide portion (23) which is provided on an upstream side of the platen roller (28) and guides an entire width of a sheet (12). A pair of sheet width guides (18a) and (18b) on an upstream side of the fixed guide portion (23) guide a sheet width. Upper guide plates (20a) and (20b) provided in the sheet guides (18a) and (18b) are shaped and located to reach an upper portion of the fixed guide portion (23).