dropdown menu on the "main menu" section

Hello,
I created a new menu("location") with couple hierarchy levels. I definitely checked all "show as expanded" for all parent items. However the drop down function does not work yet.
I can see all sub menu in the html output.

is this code error with drupal 7.18 version?
or Do I need to install the "superfish" module? I guess this theme already contained the function.

please give me some idea.

Thanks,