In this paper, we study some spectral properties of the discrete Schrόdinger operator -Δ + q defined on a locally finite connected graph with an automorphism group whose orbit space is a finite graph.The discrete Laplacian and its generalization have been explored from many different viewpoints (for instance, see [2] [4]). Our paper discusses the discrete analogue of the results on the bottom of the spectrum established by T. Kobayashi, K. Ono and T. Sunada [3] in the Riemannianmanifold-setting. § 1. Discrete Laplacians Let X = (V, E) be a locally finite connected graph without loops and multiple edges. Here V and E are, respectively, the set of vertices and the set of unoriented edges of X. In a natural manner, X is regarded as a one-dimensional CW complex. We assign a positive weight to each vertex and also to each edge by giving mappings m : V->H + and w : E ->R + . Let C 0 (V) and C 0 (E) be the space of all complex-valued functions on V and E with finite support, respectively. Define inner products on CIV) and CIE) byThe completions of C 0 (V) and C Q (E) with respect to those inner products will be denoted by L\V) and D(E), respectively. Each edge has two orientations. We use the symbol E or to represent the set of all oriented edges, so that forgetting orientation yields a twoto-one map p : E oτ -> E. Reversing orientation gives rise to an involution on E or , which we denote by e \->e. We shall use the same symbol w for