Sharepoint Designer Workflow

Im working on leave system in sharepoint and defind User group of each department like (HR gruop have HR user account and Finance have Finceace).when i desing work flow and assign UserGroup for validation like

if Created by Equals Domain\Grupname
do this
else
do this

workflow cant work properly and if i assing single user account then it work properly
like
if Created by Equals Domain\UserAct
do this
else
do this

how can i check each user account in group in workflow im using sharepoint designer for workflow