A valve seat processing machine (1) configured to process a valve seat (118) in a valve device (101) including a valve body portion (110) which forms a flow passage of fluid and a valve drive portion (120) which drives a valve element (124) capable of tightly engaging with the valve seat (118) in the valve body portion (110) includes: a base portion (10) attached to the valve body portion (110); a main body portion (20) movable relative to the base portion (10) in two different axial directions; a support portion (30) movable relative to the main body portion (20) in a drive direction of the valve element (124); a main spindle (40) rotatable relative to the support portion (30) about an axis parallel to the drive direction of the valve element (124); and a tool holder (50) configured to hold a tool (T) for processing the valve seat (118).