Holyhead coastguard said the man was hit by the caterpillar coaster on the seafront at Barmouth, Gwynedd.
The ambulance service said it was called at about 10:15 BST.
An air ambulance was sent to the scene, but the man was taken to Bronglais General Hospital in Aberystwyth by land ambulance.
A man has been taken to hospital after he was struck by a fairground ride on a north Wales promenade.