The invention provides a printer in which a lock lever comes into contact with a roller shaft of a platen roller in upper open grooves disposed in a frame and controls the position of the upper portion of the upper open grooves so that the platen roller is supported in a predetermined position of the frame and reliably comes into contact with a thermal head disposed to be opposite to the platen roller, and a lock lever member disposed so as to position a joint member for joining the upper open grooves and close to a bottom plate of the frame in a print portion in which the platen roller and a thermal head come into pressure contact with each other.