[Problems to be Solved] The invention provides a thermochromic solid writing instrument, with which crazing at a decorative part to be formed on an outer surface of a casing does not occur, and decrease in the holding power on a solid core due to a volume change of the solid core hardly occurs. [Solution] A thermochromic solid writing instrument comprising a solid core containing at least a reversible thermochromic microcapsuled pigment and a casing holding the solid core. An outer surface of the casing includes a decorative part having a display with a color, a letter, a symbol, or a figure, or a combination thereof. Further, a solid writing instrument of the invention is characterized in that the decorative part is formed of a flexible film, and/or a low heat conductivity layer is provided between the casing and the solid core.