DIFFUSION PLATE

Provided is a diffuser plate that makes it possible to mitigate unevenness of luminance or unevenness of color while suppressing speckle noise of transmitted light or reflected light. The diffuser plate of the present invention includes a microlens array having a structure that creates an optical path length difference for incident light or reflected light, the microlenses having the same effective diameter. The microlens array constitutes a basic block structure in which periodic arrangement is provided with a period of an integer multiple of the effective diameter, a two-dimensional second periodic structure having a period that is N times the period of the microlens array in the basic periodic structure is configured by a repetitive arrangement of the basic blocks, and the microlenses are set to create an optical path length difference based upon a specific arrangement within the basic block structure.