  We study U(1) and U(2) noncommutative instantons on R^2_{NC} x R^2_C based on
the ADHM construction. It is shown that a mild singularity in the instanton
solutions for both self-dual and anti-self-dual gauge fields always disappears
in gauge invariant quantities and thus physically regular solutions can be
constructed even though any projected states are not involved in the ADHM
construction. Furthermore the instanton number is also an integer.
