Abstract: The detent escapement includes a wheel 2 fitted with teeth 3, a roller 4 fitted with an impulse pallet stone 5, a blocking member in the form of a lever 6 hinged on a pin 8. The first and second arms 9 and 10 of the lever respectively carry a locking pallet stone 7 and a first actuating finger 11. An elastic member 12 is mounted on the roller 4, said member carrying a second actuating finger 14 capable of driving the first finger 11 when the roller 4 rotates in a first direction a to actuate the blocking member 6 and to move around said first finger 11 without driving it, when the roller 4 rotates in a second direction b opposite to the first. The elastic member 12 is a spring of great length including a plurality of turns 15 wounded about a centre 16.