James Van Der Beek is batting colorectal cancer ... TMZ has confirmed.

The 47-year-old actor, best known for "Dawson's Creek," was recently diagnosed with the disease -- telling People he's receiving treatment to resolve it.

Van Der Beek says -- despite the scary diagnosis -- there's reason to be optimistic. He doesn't clarify exactly what he means here, but he adds he's feeling good.

According to the American Cancer Society, colorectal cancer begins in the colon or rectum which makes up one's large intestine.

It's unclear exactly how long Van Der Beek has been battling the disease ... but, he is doing his part to help people like him afflicted with it. He's set to appear in "The Real Full Monty" -- a two-hour special where he and other big stars will strip down to raise awareness about certain types of cancer.

Van Der Beek will bare it all in the show costarring Anthony Anderson, Taye Diggs, Tyler Posey, "Dancing with the Stars" judge Bruno Tonioli, and Kansas City Chiefs defensive tackle Chris Jones.

He's also kept working in recent months despite the diagnosis ... appearing in an episode of "Walker" this year. He's also got a new movie -- "Sidelined the QB and Me" -- which is currently in post-production.