Failure to summon a legally defined interested party as a party renders the social insurance proceedings void.

The Supreme Court ruled that the Social Insurance Office's proceedings were void because the court failed to summon a specific interested party as a formal party. The cooperative argued that the party had already sought a medical certificate during the administrative control, but the court held that legal status depends on the subject matter, not subjective belief. Consequently, the lack of a summons violated procedural guarantees and necessitated the annulment of the entire process.