thank you. Following code solves my task:
Qt Code: 
  1. class DoubleDelegate: public QStyledItemDelegate
  2. {
  3.     Q_OBJECT
  4.     public:
  5.  
  6.     DoubleDelegate(QObject* parent=0) : QStyledItemDelegate(parent) { }
  7.     virtual ~DoubleDelegate() { }
  8.  
  9.     virtual QString displayText(const QVariant &value, const QLocale &locale) const
  10.     {
  11.         if (value.type() == QVariant::Double) {
  12.             return QString().sprintf("%.2f", value.toDouble()).replace('.',',');
  13.         }
  14.         return QStyledItemDelegate::displayText(value, locale);
  15.     }
  16. };
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