A printing apparatus system, comprising: a printing apparatus; and connection devices connected to the printing apparatus in multistage, wherein a device side controller is configured to: execute an authentication process in cooperation with an apparatus side controller when a signal is input thereto, the signal corresponding to a start command signal output from the printing apparatus and input to an electric resistance; and execute a level process where a voltage level of the start command signal passed the electric resistance is set to be higher than or equal to a predetermined level when the authentication process is finished, wherein the apparatus side controller is configured to store identification information assigned to each of the connection devices and number-of-stage information indicating, for each of the connection devices, which stage a connection device associated with the identification information is connected to, wherein the identification information is associated with the number-of-stage information.