To provide a baseboard with which a weight of the baseboard can be deposited to a pair of horizontal members and the baseboard can be mounted easily between the pair of horizontal members when mounting the baseboard.

A baseboard 8 comprises a baseboard body 9 having a length spread between a pair of horizontal members 3 of a building frame 1 to install a tread 5 therebetween and a pair of mounting means 10 for mounting both ends of the baseboard body 9 in a length direction to the horizontal members 3, and each of the mounting means 10 includes an engaging member 26 which is engaged to the horizontal member 3 so as to be freely disengaged therefrom for regulating movement of the baseboard body 9 outwards and upwards in the length direction. The baseboard body 9 includes terminal inner/outer walls 16, 17 which are separated inwards and outwards of the building frame 1 and between which the engaging member 26 is disposed. In lower portions of the terminal inner/outer walls 16, 17, a placement fitting part 24 is provided which is fitted to the horizontal member 3 to regulate the movement of the baseboard body 9 outwards and downwards in the length direction.