Is this SPD 2010 or 2013? How are you running the approval task?
In SP2013 workflows you can use the "Start a Task Process" activity to run an approval task on the current list item (i.e. create a task form and assign it to a specific approver) and save the outcome to a variable. By default, this activity will cause the workflow to pause until an outcome is reached; so you can react to the outcome by placing an
If... else block immediately after the task process.
Then you would configure the
If..Else block like so:
Outcome is Rejected
YesOrNoField is No
Send Notification to Recipient
You can also do this with SPD 2010 workflows but it is a little less straightforward.