A blade tensioner (1) is configured with blade shoe (2) having chain sliding face (20a), base (4) that supports base part (2a) of blade shoe (2) while allowing it to pivot freely, and blade spring (3) in which base part (3a) is fixed to tip part (2b) of blade shoe (2). Warped part (3b) provided at the tip contacts inner face (20b) of blade shoe (2), and curved part (3c) provided at the midpoint of base (4) contacts sliding face (4a) of base (4). The sliding resistance generated between warped part (3b) of blade spring (3) and inner face (20b) and between curved part (3c) and sliding face (4a) increase the natural frequency of the blade tensioner.