n addition to customizing the name of the joining table, you may also customize the column names of the keys on the table by passing additional arguments to the belongsToMany method. The third argument is the foreign key name of the model on which you are defining the relationship, while the fourth argument is the foreign key name of the model that you are joining to:
return $this->belongsToMany('App\Role', 'role_user', 'user_id', 'role_id');
Не оно?