moc.exe fails in VisualStudio

When I try to compile a Qt-project in Visual Studio 2017, I stumble upon a error in moc.exe:

Error   MSB3721 The command ""\Qt\bin\moc.exe" -i -DUNICODE -DWIN32 -DQT_THREAD_SUPPORT -DQT_CORE_LIB    -o "\Debug\Merge\moc_DbgWindow.cpp"  DbgWindow.h" exited with code 1.  

When I have a look into the project settings, section "Qt: Meta Object compiler" -> "Command line", the reason is quite clear, there a command


is specified while this path to "\Qt\bin\" does not exist.

My question: where can I change this path? I can't find a related parameter somewhere in VS2017 settings and even when I open the solution and project file in notepad, this path is defined nowhere! So where does it come from?