A printer includes a controller configured to perform a first printing process to control a thermal head to print a first image with a first density, store first print data for identifying the first image and first density data for identifying the first density into a first memory device attached to an attachment holder, when a second memory device storing second print data and second density data is attached to the attachment holder, acquire from the second memory device the second print data and the second density data stored into the second memory device by another printer, and perform a second printing process to control the thermal head to print a second image with a second density, the second image being identified based on the acquired second print data, the second density being identified based on the acquired second density data.