An aggregate median is efficiently obtained while confidentiality is kept. An order computing part generates ascending order a and descending order d within a group when a table which has been stably sorted based on a desired value attribute and a key attribute is grouped based on the key attribute. A subtracting part generates shares {a-d}, {d-a} of a-d, d-a. A bit deleting part generates shares {a′}, {d′} of a′, d′ obtained by excluding least significant bits from {a-d}, {d-a}. An equality determining part generates shares {a″}, {d″} of {a″}:={|a′=0|}, {d″}:={|d′=0|}. A format converting part (15) converts {a″}, {d″} into [a″], [d″]. A flag applying part generates shares [va], [vd] of [va]:=[v1a″], [vd]:=[v1d″]. A permutation generating part generates shares {{σa}}, {{σd}} of permutations σa, σd which sort ¬a″, ¬d″. A median computing part generates a share [x] of a vector x.