Numerical studies are performed on magnetic properties of toroidal modular systems for producing a stellarator field. For the system, which makes use of saddle coils, the rotational transform and the magnetic well are improved by making use of sectorial coils. In the ℓ = 2 stellarator using a typical sectorial coil, values of iota and magnetic well that are almost identical with those produced by a helical winding are achieved when the coil current in the equivalent helical path is twice that of the helical winding. Good accessibility is made possible by shifting or tilting the saddle coils without creating serious disturbances of the magnetic surfaces. This modular system is also studied for an ℓ = 3 stellarator. The sectorial coil is also effective in improving the rotational transform and the magnetic well in a stellarator using a modified version of a twisted coil.