In this paper, we introduce the notion of automorphic forms for GL(n, Z) ⋉ Z (m,n) and discuss invariant differential operators on the Minkowski-Euclid space. The group GL(n, R) ⋉ R (m,n) is the semidirect product of GL(n, R) and the additive group R (m,n) and is not a reductive group. The Minkowski-Euclid space is the quotient space of GL(n, R)⋉R (m,n) by O(n, R). The Minkowski-Euclid space is an important non-symmetric homogeneous space geometrically and number theoretically. We present some open problems to be solved in the future.