A reading device for holographic storage includes a light source, a light-directing component, an optical sensor and a prism. The light-directing component is disposed on the transmission path of the light beam provided by the light source and directs the light beam to get incidence at a holographic storage medium in a reading angle to generate a data beam. The optical sensor is suitable for reading the data beam and reproducing stored data. The prism is disposed between the light source and the holographic storage medium and rotatable about a rotation axis perpendicular to the transmission path of the light beam for fine-adjusting the reading angle. The prism and the light beam satisfy the following formula: {square root over (n.sup.2-sin.sup.2I.sub.1)}.times.sin A-cos A sin I.sub.1<1I.sub.1 is the angle of incidence of the light beam, A is the vertex angle between the light incident surface and the light emerging surface and n is the refractive index of the prism.