A exhalation valve 15 includes: a diaphragm 22 for opening and closing an outlet of an exhalation flow path 13 for guiding exhaled air to the outside air； a back chamber 23 that is provided to the opposite side of the exhalation flow path 13 in the diaphragm 22 and forms a space together with the diaphragm 22； and a pump unit 25 that is fixed to the circumference of the back chamber 23, for adjusting the air pressure inside the back chamber 23 by performing feeding and discharging of air to and from the back chamber 23. The diaphragm 22 closes the outlet of the exhalation flow path 13 when the air pressure inside the exhalation flow path 13 is lower than the air pressure inside the back chamber 23, and opens the outlet of the exhalation flow path 13 when the air pressure inside the exhalation flow path 13 is higher than the air pressure inside the back chamber 23. As a result, an exhalation valve and a respiratory assistance device that make accurate control possible are provided.
