The 31-year-old striker, who joined the Royals from Birmingham City exactly six years ago to the day in 1999, decided against signing a new one year contract at The Madejski and has instead moved to Portman Road on a free transfer and has penned a two-year deal with Joe Royle's side.
"We welcome Nicky Forster to Portman Road and hope he will have a thoroughly successful time here," Town Chairman David Sheepshanks told his clubs official website.
"Joe Royle was extremely keen to secure him as an experienced and wily striker who can add an extra dimension to our team.
"Nicky is the first of a number of signings that we hope to confirm over the coming days and weeks."