The present paper investigates invariant measures on nonsymmetric and rank-one type reductive real spherical homogeneous spaces \(G/H\) . To carry out, we revisit the study of a Cartan decomposition for \(G/H\) from the viewpoint of a generalization of a Cartan decomposition for semisimple symmetric spaces. Then, we introduce the notion of restricted roots associated to a Cartan decomposition and give restricted roots explicitly for each rank-one type \(G/H\) . As a consequence, we provide a characterization of an invariant measure on \(G/H\) by an integral formula based to a Cartan decomposition which is written by restricted roots.