A printer system , comprising: a host computer configured to generate and transmit print data; and a printer connected to the host computer via a communication line (L) and configured to receive the print data and perform printing based on the print data, wherein the host computer includes: a first communication interface connected to the printer ; a first display ; and a first control unit for controlling the printer configured to perform a first monitoring operation to determine operation states of the host computer and the printer and a communication state of the communication line in association with a monitored time, to store a result of the first monitoring operation associated with the monitored time and to control the first display to display the stored result of the first monitoring operation, and the printer includes: a second communication interface connected to the host computer; a second display ; and a second control unit for monitoring the host computer configured to perform a second monitoring operation to determine operation states of the host computer and the printer and a communication state of the communication line in association with a monitored time, to store a result of the second monitoring operation associated with the monitored time, and to control the second display to display the stored result of the second monitoring operation. a host computer configured to generate and transmit print data; and a printer connected to the host computer via a communication line (L) and configured to receive the print data and perform printing based on the print data, wherein the host computer includes: a first communication interface connected to the printer ; a first display ; and a first control unit for controlling the printer configured to perform a first monitoring operation to determine operation states of the host computer and the printer and a communication state of the communication line in association with a monitored time, to store a result of the first monitoring operation associated with the monitored time and to control the first display to display the stored result of the first monitoring operation, and a first communication interface connected to the printer ; a first display ; and a first control unit for controlling the printer configured to perform a first monitoring operation to determine operation states of the host computer and the printer and a communication state of the communication line in association with a monitored time, to store a result of the first monitoring operation associated with the monitored time and to control the first display to display the stored result of the first monitoring operation, and the printer includes: a second communication interface connected to the host computer; a second display ; and a second control unit for monitoring the host computer configured to perform a second monitoring operation to determine operation states of the host computer and the printer and a communication state of the communication line in association with a monitored time, to store a result of the second monitoring operation associated with the monitored time, and to control the second display to display the stored result of the second monitoring operation. a second communication interface connected to the host computer; a second display ; and a second control unit for monitoring the host computer configured to perform a second monitoring operation to determine operation states of the host computer and the printer and a communication state of the communication line in association with a monitored time, to store a result of the second monitoring operation associated with the monitored time, and to control the second display to display the stored result of the second monitoring operation. <EOS>