A needleless injection device including: - a cover, - an injection system which comprises at least one piston (32, 34), a reservoir containing an active ingredient, an injection nozzle delimiting at least one injection channel, - a body which is enveloped by the cover and which is slidably mounted relative to the cover, from bottom to top along a sliding axis, between a rest position and an injection position, - a gas generator comprising a primer, and - a percussion device that includes a striker slidably mounted along the sliding axis between a rest position in which the striker is blocked in translation by a locking means against a pre-stressed spring, and a percussion position in which the striker is released by the locking means to strike the primer of the gas generator under the action of said spring characterized in that the locking means of the striker includes at least: - a lug which protrudes from a peripheral face of the striker along an axis generally perpendicular to the sliding axis and which has a first bearing ramp, - a retaining tab which is secured to the cover and which has a second bearing ramp arranged facing said first bearing ramp, said ramps (72a, 86a) being designed to cooperate together in order to radially drive the retaining tab under the effect of the push of the striker, from a retaining position in which the first ramp axially bears on the second ramp so that the retaining tab opposes the sliding of the striker to a release position in which the retaining tab is spaced apart in order to release the striker, and - an obstruction which is secured to the body and which is designed to constrain the retaining tab in its retaining position, when the body occupies its rest position, and to release the retaining tab in its release position when the body occupies its injection position. - a cover, - an injection system which comprises at least one piston (32, 34), a reservoir containing an active ingredient, an injection nozzle delimiting at least one injection channel, - a body which is enveloped by the cover and which is slidably mounted relative to the cover, from bottom to top along a sliding axis, between a rest position and an injection position, - a gas generator comprising a primer, and - a percussion device that includes a striker slidably mounted along the sliding axis between a rest position in which the striker is blocked in translation by a locking means against a pre-stressed spring, and a percussion position in which the striker is released by the locking means to strike the primer of the gas generator under the action of said spring - a lug which protrudes from a peripheral face of the striker along an axis generally perpendicular to the sliding axis and which has a first bearing ramp, - a retaining tab which is secured to the cover and which has a second bearing ramp arranged facing said first bearing ramp, said ramps (72a, 86a) being designed to cooperate together in order to radially drive the retaining tab under the effect of the push of the striker, from a retaining position in which the first ramp axially bears on the second ramp so that the retaining tab opposes the sliding of the striker to a release position in which the retaining tab is spaced apart in order to release the striker, and - an obstruction which is secured to the body and which is designed to constrain the retaining tab in its retaining position, when the body occupies its rest position, and to release the retaining tab in its release position when the body occupies its injection position.