A blade tensioner of a blade tensioner system for a chain that drivingly connects a drive shaft to a driving shaft in an engine, that improves the chain-damping efficiency in a blade tensioner applied to the chain within an engine, prevents the sideways tilt of the blade tensioner during operation, in a blade tensioner applied to the chain in an engine, and provides a blade tensioner with a functionality that allows it to transversely guide a chain along the chain sliding face in a blade shoe, while maintaining the flexural deformability (i.e., the flexibility) of the blade shoe.