A hydraulic lash adjuster comprising: a hollow plunger slidably fitted in a bottomed cylindrical body, with its head portion protruding from an open end of the body; a low-pressure chamber for storing oil therein, the low-pressure chamber formed in the plunger utilizing an interior of the plunger and in communication with an exterior and an exterior thereof via a communication hole formed in the head portion, a high-pressure chamber to be charged with oil, the high-pressure chamber formed between a bottom of the body and a bottom of the plunger in the body; an oil supply hole, formed in a peripheral wall of the plunger, for ejecting oil into the low-pressure chamber and for constituting an oil supply passage; a biasing means disposed between the bottom of the body and a bottom of the plunger; and a valve mechanism disposed at a bottom of the plunger and adapted to open a valve to allow for a flow of oil from the low-pressure chamber to the high-pressure chamber when the plunger is extended by a restoring force of the biasing means, the lash adjuster characterized in that: an impingement area of the inner periphery of the plunger subjected to impingement of oil ejected from the oil supply hole is inclined to fall in the direction of the ejected oil as the area nears the plunger's head portion; the plunger is provided on its inner periphery with a pair of inclined areas opposing each other across an inner diameter of the plunger; the pair of inclined areas come closer to each other as they extend away from the head portion of the plunger in the axial direction of the plunger; the oil supply hole is formed in one of the paired inclined areas with its opening facing an interior of the low-pressure chamber; and the oil supply hole is so set as to direct the orientation of the oil supply hole to the other inclined area of the paired inclined areas so that the other inclined area serves as the impingement area. a hollow plunger slidably fitted in a bottomed cylindrical body, with its head portion protruding from an open end of the body; a low-pressure chamber for storing oil therein, the low-pressure chamber formed in the plunger utilizing an interior of the plunger and in communication with an exterior and an exterior thereof via a communication hole formed in the head portion, a high-pressure chamber to be charged with oil, the high-pressure chamber formed between a bottom of the body and a bottom of the plunger in the body; an oil supply hole, formed in a peripheral wall of the plunger, for ejecting oil into the low-pressure chamber and for constituting an oil supply passage; a biasing means disposed between the bottom of the body and a bottom of the plunger; and a valve mechanism disposed at a bottom of the plunger and adapted to open a valve to allow for a flow of oil from the low-pressure chamber to the high-pressure chamber when the plunger is extended by a restoring force of the biasing means, the lash adjuster characterized in that: an impingement area of the inner periphery of the plunger subjected to impingement of oil ejected from the oil supply hole is inclined to fall in the direction of the ejected oil as the area nears the plunger's head portion; the plunger is provided on its inner periphery with a pair of inclined areas opposing each other across an inner diameter of the plunger; the pair of inclined areas come closer to each other as they extend away from the head portion of the plunger in the axial direction of the plunger; the oil supply hole is formed in one of the paired inclined areas with its opening facing an interior of the low-pressure chamber; and the oil supply hole is so set as to direct the orientation of the oil supply hole to the other inclined area of the paired inclined areas so that the other inclined area serves as the impingement area. an impingement area of the inner periphery of the plunger subjected to impingement of oil ejected from the oil supply hole is inclined to fall in the direction of the ejected oil as the area nears the plunger's head portion; the plunger is provided on its inner periphery with a pair of inclined areas opposing each other across an inner diameter of the plunger; the pair of inclined areas come closer to each other as they extend away from the head portion of the plunger in the axial direction of the plunger; the oil supply hole is formed in one of the paired inclined areas with its opening facing an interior of the low-pressure chamber; and the oil supply hole is so set as to direct the orientation of the oil supply hole to the other inclined area of the paired inclined areas so that the other inclined area serves as the impingement area.