The ScrumMaster is a servant-leader for the Scrum Team. The Scrum Master exists to serve the team, puts the needs of the team first. This with the firm belief that you get the best out of people when you empower them.
A Project Manager is responsible to meet the project objective. Within Scrum there is no such role for a Project Manager. The role that comes closest is the Product Owner, who should maximize value from the product.
One of these exists in Scrum, the other does not... :)
The Agile Daily Standup - AgileDad