A printer comprising: a printing unit configured to perform printing on a sheet while conveying the sheet based on a printing schedule; a circulation conveyer including a circulation route and configured in duplex printing to receive the sheet with a front side printed from the printing unit and convey the received sheet along the circulation route; a paper feeder including a paper feeding route for conveying an unprinted sheet, and a common conveyer configured to convey the unprinted sheet conveyed along the paper feeding route to the printing unit and convey the sheet with the front side printed conveyed along the circulation route to the printing unit; and a controller configured to control the printing unit, the paper feeder, and the circulation conveyer, wherein the circulation route includes a section in which the sheet with the front side printed is conveyed at a reverse conveying speed and transferred to the common conveyer, and the controller is configured in the duplex printing to: determine the reverse conveying speed corresponding to the printing schedule based on a printing condition; determine a switching timing corresponding to the printing schedule; and switch an operation of the common conveyer at the determined switching timing between a paper feeding conveying operation and a paper refeeding conveying operation, the paper feeding conveying operation being for receiving the unprinted sheet at a paper feeding conveying speed and conveying the unprinted sheet to the printing unit, the paper refeeding conveying operation being for receiving the sheet with the front side printed at the determined reverse conveying speed and conveying the sheet with the front side printed to the printing unit. a printing unit configured to perform printing on a sheet while conveying the sheet based on a printing schedule; a circulation conveyer including a circulation route and configured in duplex printing to receive the sheet with a front side printed from the printing unit and convey the received sheet along the circulation route; a paper feeder including a paper feeding route for conveying an unprinted sheet, and a common conveyer configured to convey the unprinted sheet conveyed along the paper feeding route to the printing unit and convey the sheet with the front side printed conveyed along the circulation route to the printing unit; and a controller configured to control the printing unit, the paper feeder, and the circulation conveyer, wherein the circulation route includes a section in which the sheet with the front side printed is conveyed at a reverse conveying speed and transferred to the common conveyer, and the controller is configured in the duplex printing to: determine the reverse conveying speed corresponding to the printing schedule based on a printing condition; determine a switching timing corresponding to the printing schedule; and switch an operation of the common conveyer at the determined switching timing between a paper feeding conveying operation and a paper refeeding conveying operation, the paper feeding conveying operation being for receiving the unprinted sheet at a paper feeding conveying speed and conveying the unprinted sheet to the printing unit, the paper refeeding conveying operation being for receiving the sheet with the front side printed at the determined reverse conveying speed and conveying the sheet with the front side printed to the printing unit. determine the reverse conveying speed corresponding to the printing schedule based on a printing condition; determine a switching timing corresponding to the printing schedule; and switch an operation of the common conveyer at the determined switching timing between a paper feeding conveying operation and a paper refeeding conveying operation, the paper feeding conveying operation being for receiving the unprinted sheet at a paper feeding conveying speed and conveying the unprinted sheet to the printing unit, the paper refeeding conveying operation being for receiving the sheet with the front side printed at the determined reverse conveying speed and conveying the sheet with the front side printed to the printing unit.