Provided is a tube holding member including: an insertion portion that is inserted into an insertion groove that has a first width in a width direction; and a pair of arm portions that project from the insertion groove, in which the insertion portion includes a pair of wall portions that hold a tube in a pinched state, and a coupling portion that couples the pair of wall portions, the coupling portion is elastically deformable, and the pair of wall portions are disposed to be in contact with the insertion groove such that the pair of wall portions have a second width that is longer than the first width in the width direction in a state in which the insertion portion is not inserted into the insertion groove and have the first width in the width direction in a state in which the insertion portion is inserted into the insertion groove.