Oil seal for reciprocation motion

An oil seal for reciprocation motion including a seal main body, a resin backup ring, and a holding member. The seal main body includes a seal lip that can be in sliding contact with a reciprocating shaft. The backup ring is disposed such as to support the seal lip from the atmosphere side to ensure durability of the seal lip. In the backup ring, at least a single annular groove is provided on the inner peripheral surface opposing the reciprocating shaft. The annular groove can hold a lubricating material. The holding member holds the backup ring between the holding member and the seal main body in a sandwiched-state. The inner peripheral surface of the backup ring forms a taper that increases in diameter from a sealed side towards an atmosphere side in the axial direction.