A printer 10 provided with communication section 11 for obtaining print information necessary to print, from plural host devices 30 through transmission route 50, is characterized by comprising; a host ID getter 12 to get host ID able to distinguish host device which outputted said print information from other host device, with using the print information itself obtained; a trouble detector 14 able to detect trouble with judging whether printing based on said print information is possible or not; a presenter 16 to present said host ID obtained by said host ID getter 12 when printing was not judged possible by said trouble detector 14.