A systematic study on the ground-state structure of He isotopes (including ¹⁰He) is presented through a new method developed on the basis of antisymmetrized molecular dynamics (AMD), the generator coordinate method (GCM), and the stochastic variational method (SVM). In this approach, variational calculations are carried out by means of the GCM with the AMD wave functions produced by means of the SVM. A role of the t+t cluster component is examined with the present method, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "⁴He+valence neutrons" structure.