According to the authorities, the suspect admitted that he wanted the Kagawa assembly to repeal a recent ordinance restricting video game playing time among children.
Police arrested a 21-year-old male suspect on Wednesday after he allegedly sent a threatening message to Kagawa prefectural assembly member Ichirō Ōyama.
The Kagawa Bar Association requested an immediate repeal of the ordinance in late May.
The ordinance took effect on April 1, following discussions in the assembly and a majority vote.