The invention enables a platen roller, which is part of a platen roller mechanism having a simple mechanism, to be replaced, and to enable the size and weight of a printer to be reduced. This platen roller holding mechanism comprises: a printer body; a thermal head that is fixed to the printer body, and prints on sheet-like members; and a platen roller that is positioned so as to face the thermal head, and presses the sheet-like members against the thermal head. Furthermore, the platen roller holding mechanism rotatably holds the platen roller in the printer body. The platen roller holding mechanism is characterized by having: a sheet-like member support part that supports the sheet-like members; and a sheet-like member detector support part that supports a detector that detects the sheet-like members, and is integrated with the sheet-like member support part.