A portable thermal printer includes a housing and an anti-skew unit. The housing is provided with a thermal printer head and a platen roller, and is configured to convey a paper between the thermal printer head and the platen roller. The anti-skew unit inside the housing is configured to contact both side edges of the paper in a width direction to prevent the paper, which is being conveyed, from skewing, and the setting of the width of the paper by the anti-skew unit is configured to be adjustable from outside the housing.