A printing unit, comprising: a platen roller configured to convey a recording sheet; a thermal head configured to perform printing on the recording sheet through press contact with an outer peripheral surface of the platen roller; a motor configured to serve as a drive source of the platen roller; and a frame configured to support the platen roller in a rotatable manner, wherein the frame includes: a motor support portion configured to support the motor; a base portion which is connected to the motor support portion, and extends in an axial direction of the platen roller; mounting portions which are attached to a member on which the printing unit is to be mounted; a protruding portion which protrudes from the base portion; and a rib which is provided between the motor support portion and the mounting portions, and extends so as to connect the protruding portion and the base portion to each other, the base portion includes a guide surface configured to guide the recording sheet toward the thermal head, and the guide surface is inclined with respect to a direction normal to a head surface of the thermal head; characterized in that wherein the printing unit further comprises a fastening portion which protrudes from the base portion, the fastening portion and the protruding portion being provided between the motor support portion and the mounting portions. a platen roller configured to convey a recording sheet; a thermal head configured to perform printing on the recording sheet through press contact with an outer peripheral surface of the platen roller; a motor configured to serve as a drive source of the platen roller; and a frame configured to support the platen roller in a rotatable manner, wherein the frame includes: a motor support portion configured to support the motor; a base portion which is connected to the motor support portion, and extends in an axial direction of the platen roller; mounting portions which are attached to a member on which the printing unit is to be mounted; a protruding portion which protrudes from the base portion; and a rib which is provided between the motor support portion and the mounting portions, and extends so as to connect the protruding portion and the base portion to each other, a motor support portion configured to support the motor; a base portion which is connected to the motor support portion, and extends in an axial direction of the platen roller; mounting portions which are attached to a member on which the printing unit is to be mounted; a protruding portion which protrudes from the base portion; and a rib which is provided between the motor support portion and the mounting portions, and extends so as to connect the protruding portion and the base portion to each other, the base portion includes a guide surface configured to guide the recording sheet toward the thermal head, and the guide surface is inclined with respect to a direction normal to a head surface of the thermal head; characterized in that wherein the printing unit further comprises a fastening portion which protrudes from the base portion, the fastening portion and the protruding portion being provided between the motor support portion and the mounting portions.