Yes, it's a 306. One of Singer's all time great machines. This one looks like it's in fine shape, that even looks like a new belt.
One of the more intriguing things about this line of machines, the 206, 306, 319 and 320 are the parts that move on the outside of the machine. This arm moves the mechanism that swings the needle for the zig zag and embroidery stitches. It's attached to another mechanism on the front that's a fork that moves back and forth to move the needle bar. You can just see the back of that fork mechanism just below the end of the arm. There is a dial that spins that holds the removable cam and the cam follower, also on the outside of the machine moves up and down in the cam. These moving parts on the outside of the machines is one of things I love about these machines.