An electro hydrostatic actuator system (1, 10, 11, 100) for retracting/extending a landing gear of an aircraft, comprising: a plurality of hydraulic actuators (21, 22, 23) configured to sequentially receive, for operation thereof, a supply of operation oil in retraction or extension of the landing gear; and a plurality of hydraulic supply sources (31, 32, 51, 52) provided in parallel to each other such that the operation oil is supplied to each hydraulic actuator (21, 22, 23), wherein each hydraulic supply source (31, 32, 51, 52) includes a single hydraulic pump (33, 53) configured to discharge the operation oil, and a single electric motor (34, 54) configured to drive the hydraulic pump (33, 53), the hydraulic supply sources (31, 32, 51, 52) together supply the operation oil sequentially to the hydraulic actuators (21, 22, 23) in a normal state of the hydraulic supply sources (31, 32, 51, 52), and when at least one of the hydraulic supply sources (31, 32, 51, 52) is failed, at least one hydraulic supply source (31, 32, 51, 52) other than the failed one of the hydraulic supply sources (31, 32, 51, 52) supplies the operation oil sequentially to the hydraulic actuators (21, 22, 23), characterized in that the hydraulic actuators (21, 22, 23) are different from each other in operation oil supply conditions required for the operation of the hydraulic actuators (21, 22, 23), and an operation oil supply capacity of each hydraulic supply source (31, 32, 51, 52) required for sequentially operating the hydraulic actuators (21, 22, 23) to retract or extend the landing gear is set based on the supply conditions, a supply capacity of each hydraulic supply source (31, 32, 51, 52) is set so as to be lower than the required supply capacity of each hydraulic supply source (31, 32, 51, 52), in the normal state of the hydraulic supply sources (31, 32, 51, 52), the hydraulic pump (33, 53) of each hydraulic supply source (31, 32, 51, 52) has a predetermined rotational speed to supply the operation oil sequentially to the hydraulic actuators (21, 22, 23), and when at least one of the hydraulic supply sources (31, 32, 51, 52) is failed, the hydraulic pump (33, 53) of at least one hydraulic supply source (31, 32, 51, 52) other than the failed one of the hydraulic supply sources (31, 32, 51, 52) has a rotational speed higher than the predetermined rotational speed. a plurality of hydraulic actuators (21, 22, 23) configured to sequentially receive, for operation thereof, a supply of operation oil in retraction or extension of the landing gear; and a plurality of hydraulic supply sources (31, 32, 51, 52) provided in parallel to each other such that the operation oil is supplied to each hydraulic actuator (21, 22, 23), wherein each hydraulic supply source (31, 32, 51, 52) includes a single hydraulic pump (33, 53) configured to discharge the operation oil, and a single electric motor (34, 54) configured to drive the hydraulic pump (33, 53), the hydraulic supply sources (31, 32, 51, 52) together supply the operation oil sequentially to the hydraulic actuators (21, 22, 23) in a normal state of the hydraulic supply sources (31, 32, 51, 52), and when at least one of the hydraulic supply sources (31, 32, 51, 52) is failed, at least one hydraulic supply source (31, 32, 51, 52) other than the failed one of the hydraulic supply sources (31, 32, 51, 52) supplies the operation oil sequentially to the hydraulic actuators (21, 22, 23), the hydraulic actuators (21, 22, 23) are different from each other in operation oil supply conditions required for the operation of the hydraulic actuators (21, 22, 23), and an operation oil supply capacity of each hydraulic supply source (31, 32, 51, 52) required for sequentially operating the hydraulic actuators (21, 22, 23) to retract or extend the landing gear is set based on the supply conditions, a supply capacity of each hydraulic supply source (31, 32, 51, 52) is set so as to be lower than the required supply capacity of each hydraulic supply source (31, 32, 51, 52), in the normal state of the hydraulic supply sources (31, 32, 51, 52), the hydraulic pump (33, 53) of each hydraulic supply source (31, 32, 51, 52) has a predetermined rotational speed to supply the operation oil sequentially to the hydraulic actuators (21, 22, 23), and when at least one of the hydraulic supply sources (31, 32, 51, 52) is failed, the hydraulic pump (33, 53) of at least one hydraulic supply source (31, 32, 51, 52) other than the failed one of the hydraulic supply sources (31, 32, 51, 52) has a rotational speed higher than the predetermined rotational speed.