A back surface side of a thermal head is made compact, and a depth dimension as a whole is made smaller. There is provided a thermal printer (1) including: a main body frame (2); a thermal head (4) swingably mounted to the main body frame (2); a platen roller (6) disposed to be opposed to a printing surface (4a) of the thermal head (4), for sandwiching a thermal paper with the thermal head (4) to feed the thermal paper; a lock arm (5) swingably mounted to the main body frame (2), for locking the platen roller (6) with the main body frame (2) by pressing a shaft bearing (9) which rotatably supports the platen roller (6) against the thermal head (4); a first spring (7) disposed between the lock arm (5) and the thermal head (4), for biasing the platen roller (6) in a direction in which the platen roller (6) moves toward the thermal head (4) ; and a second spring (8) disposed between the thermal head (4) and the main body frame (2), for biasing the thermal head (4) in a direction in which the thermal head (4) comes into close contact with the platen roller (6), in which the first spring (7) is disposed so that the first spring (7) applies a biasing force to the lock arm (5) at a position where the first spring (7) is closer to a swing center (3) of the lock arm (5) than the second spring (8) is.