A printing unit , comprising: a platen roller , which extends in an axial direction, and is configured to convey a recording sheet (P); a thermal head configured to perform printing on the recording sheet (P) through press contact with an outer peripheral surface of the platen roller ; a support plate , which is arranged on a side opposite to the platen roller across the thermal head , and is configured to support the thermal head ; a frame , which includes a rear plate portion arranged on a side opposite to the platen roller across the support plate , and is configured to support both ends of the support plate in the axial direction; at least one urging member , which is arranged between the rear plate portion and the support plate , and is configured to press the support plate to the platen roller side; and a protruding portion , which is formed on the support plate to protrude from the support plate to the rear plate portion side, and is configured to regulate displacement of a predetermined urging member of the at least one urging member , wherein a recessed portion is formed in a portion of the rear plate portion opposed to the protruding portion in a thickness direction of the support plate , wherein the recessed portion has a depth larger than a height of the protruding portion , and characterized in that the recessed portion is configured to accommodate the protruding portion in a state in which the protruding portion is held in non-contact with the rear plate portion , in a case that the support plate bends due to an impact on the printing unit so that the support plate is brought into contact with a portion of the rear plate portion outside the recessed portion . a platen roller , which extends in an axial direction, and is configured to convey a recording sheet (P); a thermal head configured to perform printing on the recording sheet (P) through press contact with an outer peripheral surface of the platen roller ; a support plate , which is arranged on a side opposite to the platen roller across the thermal head , and is configured to support the thermal head ; a frame , which includes a rear plate portion arranged on a side opposite to the platen roller across the support plate , and is configured to support both ends of the support plate in the axial direction; at least one urging member , which is arranged between the rear plate portion and the support plate , and is configured to press the support plate to the platen roller side; and a protruding portion , which is formed on the support plate to protrude from the support plate to the rear plate portion side, and is configured to regulate displacement of a predetermined urging member of the at least one urging member , wherein a recessed portion is formed in a portion of the rear plate portion opposed to the protruding portion in a thickness direction of the support plate , wherein the recessed portion has a depth larger than a height of the protruding portion , and characterized in that the recessed portion is configured to accommodate the protruding portion in a state in which the protruding portion is held in non-contact with the rear plate portion , in a case that the support plate bends due to an impact on the printing unit so that the support plate is brought into contact with a portion of the rear plate portion outside the recessed portion . <EOS>