A hose clamp includes a clamp main body including a ring portion and a pair of knob portions; and a holder. The holder includes a main body portion, a pair of holding walls, and an operation portion. An inner surface on a distal end side of one holding wall includes a protrusion that protrudes more largely inward than an inner surface on a distal end side of other holding wall. And in a state where the pair of knob portions are close to each other, a distal end of one knob portion in a peripheral direction is engaged with the inner surface of the one holding wall, and the other knob portion is engaged with the inner surface of the other holding wall, so that the ring portion is kept in a diameter-increased state.