To provide a well plate with which assay can be carried out without being restricted by the amount of a used reagent to be administered.

Wells 30 for the reagent are constituted of outside wells each at the nearest position to each of neighboring two sides of a rectangular well plate body 10, and inside wells 30d surrounded by wells 20 for specimens integrally formed in the well plate body 10 in a matrix shape. The capacities of the outside wells 30a in the row direction, the outside wells 30b in the line direction and the outside wells 30c at the corner parts, constituting the outside wells are regulated so as to have the same capacities as those of the inside wells 30d.