diff --git a/application/application.cpp b/application/application.cpp
new file mode 100644
index 0000000..833904b
--- /dev/null
+++ b/application/application.cpp
@@ -0,0 +1,31 @@
+#include "application.h"
+
+Application::Application(int &argc, char **argv)
+    :QApplication(argc, argv)
+{
+    m_single = new QSharedMemory("ShredMemoryForOneInstanceOfProdejnaApp", this);
+}
+
+Application::~Application()
+{
+    if (m_single->isAttached())
+    {
+        m_single->detach();
+    }
+}
+
+bool Application::lock()
+{
+    if (m_single->attach(QSharedMemory::ReadOnly))
+    {
+        m_single->detach();
+        return false;
+    }
+
+    if (m_single->create(1))
+    {
+        return true;
+    }
+
+    return false;
+}
diff --git a/application/application.h b/application/application.h
new file mode 100644
index 0000000..259e5b0
--- /dev/null
+++ b/application/application.h
@@ -0,0 +1,21 @@
+#ifndef APPLICATION_H
+#define APPLICATION_H
+
+#include <QApplication>
+#include <QSharedMemory>
+
+class Application : public QApplication
+{
+    Q_OBJECT
+
+public:
+    Application(int &argc, char **argv);
+    ~Application();
+
+    bool lock();
+
+private:
+    QSharedMemory *m_single;
+};
+
+#endif // APPLICATION_H
diff --git a/application/application.pro b/application/application.pro
index 9f28ab0..d7edcc3 100644
--- a/application/application.pro
+++ b/application/application.pro
@@ -28,10 +28,12 @@ win32 {
 
 SOURCES += main.cpp\
         mainwindow.cpp \
-    logindialog.cpp
+    logindialog.cpp \
+    application.cpp
 
 HEADERS  += mainwindow.h \
-    logindialog.h
+    logindialog.h \
+    application.h
 
 FORMS    += mainwindow.ui \
     logindialog.ui
diff --git a/application/main.cpp b/application/main.cpp
index d15d3a0..4fda4ee 100644
--- a/application/main.cpp
+++ b/application/main.cpp
@@ -3,6 +3,9 @@
 #include <QDesktopWidget>
 #include <QTranslator>
 #include <QLibraryInfo>
+#include <QMessageBox>
+
+#include "application.h"
 
 #ifdef _WIN32
 #include <Windows.h>
@@ -10,7 +13,13 @@
 
 int main(int argc, char *argv[])
 {
-    QApplication a(argc, argv);
+    Application a(argc, argv);
+
+    if (!a.lock())
+    {
+        QMessageBox::warning(NULL, "Prodejna is running", "Prodejna is allready running. Only one instance can be started.");
+        return -42;
+    }
 
 #ifdef _WIN32
     QString exePath = a.applicationDirPath();