The invention provides a portable radiation imaging apparatus and a portable radiation imaging system which can prevent reception failure of additional orders while receiving imaging orders by means of wireless communication. A portable X-ray imaging apparatus has an electronic cassette and a console capable of receiving an imaging order. The console has a wireless communication section, a trigger signal obtaining section, a connection determining section, a switching section, and a delivery requesting section. The wireless communication section receives radio waves and connects itself to an access point (AP). The trigger signal obtaining section obtains a trigger signal while the mobile radiography unit stands still. At the time of obtaining the trigger signal, the connection determining section determines one of the APs as an appropriate AP based on field intensity. The switching section switches the connection to the appropriate AP. Then, the delivery requesting section transmits a delivery request for the imaging order.