A rapidly erectable four cornered shelter frame for use with a canvas top has a pair of foldable end frame members with corner posts and an end joint at the upper end of each having a pair of upwardly inclined end rafters connected by an end ridge joint which has a ridge member projecting perpendicularly to the rafters. A foldable intermediate frame member has ground support posts with side joints at the upper ends having a pair of upwardly inclined intermediate rafters connected by an intermediate ridge joint to which each of the end frame members also connects. Eave members extend from each side joint to releasably connect to each end joint, which also incorporates mechanism to lock the end rafters in extended position, while permitting them to fold down to a position in parallelism with the corner posts when unlocked. The end ridge joints incorporate mechanism to lock the ridge members in extended position, while permitting them to fold down to a position in parallelism with the corner posts when unlocked, and side joints incorporate mechanism to lock the intermediate rafters in extended position, while permitting them to fold down to a position in parallelism with the intermediate ground support posts when unlocked.