A printing unit, comprising: a platen roller, which extends in an axial direction, and is 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 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; a thermal head configured to perform printing on the recording sheet 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.