public function addProduct($product_class_id, $quantity)
    {
        $objProduct = new SC_Product_Ex();
        $arrProduct = $objProduct->getProductsClass($product_class_id);
        $productTypeId = $arrProduct['product_type_id'];
        $find = false;
        $max = $this->getMax($productTypeId);

        for ($i = 0; $i <= $max; $i++) {
            if ($this->cartSession[$productTypeId][$i]['id'] == $product_class_id) {
                $val = $this->cartSession[$productTypeId][$i]['quantity'] + $quantity;
                if (strlen($val) <= INT_LEN) {
                    $this->cartSession[$productTypeId][$i]['quantity'] += $quantity;
                }
                $find = true;
            }
        }
        if (!$find) {
            //追加↓
            $this->delAllProducts($productTypeId)
            //追加↑
            $this->cartSession[$productTypeId][$max+1]['id'] = $product_class_id;
            $this->cartSession[$productTypeId][$max+1]['quantity'] = $quantity;
            $this->cartSession[$productTypeId][$max+1]['cart_no'] = $this->getNextCartID($productTypeId);
        }
    }