>In oncreate(); write this line->
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
>then implement below method in that class
@Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case android.R.id.home: // app icon in action bar clicked; go home onBackPressed(); return true; default: return super.onOptionsItemSelected(item); } }

Firstly Use this:
> ActionBar bar = getSupportActionBar();
> bar.setDisplayHomeAsUpEnabled(true);
Then set operation of button click in onOptionsItemSelected method
@Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case android.R.id.home: finish(); return true; default: return super.onOptionsItemSelected(item); } }