For an undirected/directed hypergraph G = (V, E), its Laplacian L G : R V → R V is defined such that its "quadratic form" x L G (x) captures the cut information of G. In particular,In this paper, we present a polynomial-time algorithm that, given an undirected/directed hypergraph G on n vertices, constructs an -spectral sparsifier of G with O(n 3 log n/ 2 ) hyperedges/hyperarcs.The proposed spectral sparsification can be used to improve the time and space complexities of algorithms for solving problems that involve the quadratic form, such as computing the eigenvalues of L G , computing the effective resistance between a pair of vertices in G, semisupervised learning based on L G , and cut problems on G. In addition, our sparsification result implies that any submodular function f : 2 V → R + with f (∅) = f (V ) = 0 can be concisely represented by a directed hypergraph. Accordingly, we show that, for any distribution, we can properly and agnostically learn submodular functions f : 2 V → [0, 1] with f (∅) = f (V ) = 0, with O(n 4 log(n/ )/ 4 ) samples.