Provided is a printer that employs a platen roller as conveying means, for which the accuracy of the assembly of the constituents of a drive transmission mechanism that drives a platen roller is increased, and the heat releasing function of a motor that is a drive source is also improved, so that downsizing and increasing output can be coped with. Therefore, according to the present invention, a printer comprises: a platen roller, for conveying a recording sheet, a print head, arranged opposite the platen roller, a drive unit, for rotating the platen roller, and a main frame, including a pair of side walls that can rotatably support the platen roller, wherein the drive unit includes: a motor; idler gears, for transmitting a rotational force provided by the motor to the platen roller; and a gear fitting member, integrally formed with gear support shafts that support the idler gears, wherein the motor and idler gears are capable of being mounted in the main frame while attached to the gear fitting member, and wherein a drive gear of the motor and the idler gears are stored in a space defined by the gear fitting member and one of the side walls of the main frame.