Ben Affleck has completed a 40-day stay at a California rehab facility for alcohol addiction ... and is now in outpatient care.
Affleck posted a message Thursday, saying, "The support I have received from my family, colleagues and fans means more to me than I can say. It's given me the strength and support to speak about my illness with others."
TMZ broke the story ... Jennifer Garner staged an intervention at Ben's Pacific Palisades home back in August. Garner then drove Ben to a Malibu facility where he's been in treatment ever since, with occasional breaks for work and trips to his home gym.
Ben continues, "Battling any addiction is a lifelong and difficult struggle ... As I've had to remind myself, if you have a problem, getting help is a sign of courage, not weakness or failure."