#--------------------------------------------------------------------------
  # ● 执行买入
  #--------------------------------------------------------------------------
  def do_buy(number)
    $game_party.lose_gold(number * buying_price)
    $game_party.gain_item(@item, number)
  end
  #--------------------------------------------------------------------------
  # ● 执行卖出
  #--------------------------------------------------------------------------
  def do_sell(number)
    $game_party.gain_gold(number * selling_price)
    $game_party.lose_item(@item, number)
  end