A program update device that is provided in a vehicle in which a battery can be charged from the outside and updates a software program used in the vehicle includes a charging time acquiring unit that acquires the charging time of the battery, an update time acquiring unit that acquires the time required to rewrite the program, a comparison unit that compares the charging time acquired by the charging time acquiring unit and the program rewrite time acquired by the update time acquiring unit, and an update unit that rewrites the program on the basis of the comparison result of the comparison unit. According to this structure, it is possible to appropriately determine a program which can be updated within the battery charging time and reliably update the program while the vehicle is being charged.