A stand pipe is disposed so as to be fitted with the inner periphery surface of a piston rod with a hollow structure and a reservoir is incorporated into the inside of the stand pipe, whereby it becomes possible to reduce the size of an EHA device. Additional air intake openings are formed on the actuating element and define an additional flow path through the valve chamber. The medical device has a camera lumen having a sealed window at one end thereof attached thereto, and a separate camera which is insertable into the camera lumen and is removable from the camera lumen. An In composition ratio in the group III elements of the second layer is higher than an In composition ratio in the group III elements of the first layer. At least a portion of the data in the first memory device is written to a third memory device when a predetermined amount of data has been accumulated in the first memory device.