Chain tensioner

A chain tensioner comprising:

• a tensioner body with a plunger bore that is open on one side;
• a cylindrical plunger slidably inserted in the plunger bore;
• and
• a biasing member that biases the plunger in an extension direction,
• the plunger including on an outer circumferential surface thereof a plurality of raised portions of the plunger with which a locking member engages,
• the plunger bore being provided with a locking member holding part on one side that is open, the locking member holding part being open toward a center axis of the plunger and holding the locking member,
• the locking member holding part being provided with an inclined surface at least at one end in a plunger entry direction in which the plunger enters into the plunger bore, the inclined surface becoming progressively shallower in the plunger entry direction,
• the locking member holding part is formed in a ring,
• the locking member is formed into an endless ring shape,
• the locking member forces the plunger in a direction that causes the diameter of the locking member to contract,
• the locking member being an elastic member to deform elastically in a cross section inside the locking member holding part to have a cross sectional shape conforming to the inclined surface of the locking member holding part when engaging with the raised portions of the plunger.