Manhole type base station, mobile communication system having the base station and hand-off control method in the mobile communication system

A larger service area can be ensured, and a trouble such as a reduction in service area or the interruption of communication which is caused when an obstructive exists on a manhole cover is quickly prevented. A wall portion that defines a space in which a transmit/receive antenna is disposed has such a slope as to expand the space from a base station unit toward an upper surface portion of the manhole cover, and an angle of slope varies depending on the dimensions of the service area. Also, when the existence of the obstructive on the manhole cover is detected by use of a pressure sensor or an electric wave sensor, the control of the communication operation of a mobile station is switched to another base station without calculating or processing an electric field intensity in the base station.