Ryuji Kimura filed the lawsuit in the Kobe district court last June, claiming he could not run for election held on July 10 due to his age and inability to prepare a 3 million yen ($22,339) deposit, the report said, citing the case record.
According to the record, Kimura claimed the election law violates the Constitution, which stipulates equality under the law among other provisions.
The court dismissed the claim, in which the 24-year-old suspect sought 100,000 yen in damages for the mental anguish he had suffered, said the Yomiuri report.
Kimura appealed to the Osaka High Court against this ruling, and a decision was scheduled for May this year, it said.
Japanese authorities searched Kimura's home on Sunday in Kawanishi city in Hyogo after he was arrested on the scene after allegedly attempting to attack Kishida with an explosive object during his election speech in Wakayama City. He has not yet been charged.