A flow passage switching unit includes side-by-side arranged rotary valve parts. The valve part includes a casing, side walls, a peripheral wall, first fluid ports, a second fluid port, a rotary shaft, and a valving element. A flow passage, through which the first fluid ports and the second fluid port selectively communicate, is formed by rotation of the valving element. The unit includes a driving mechanism driving each valving element by its corresponding predetermined rotation angle. The driving mechanism includes one driving source, and a motive power transmission member transmitting rotation motive power of the driving source respectively to the valve parts. Motive power of the driving source is transmitted to each rotary shaft of the valve parts to drive each valving element to a position, which position of the valving element relative to the first and second fluid ports is different from one another among the valve parts.