A power tool comprising: a tool unit having a rotary spindle; characterised by a plurality of unit support members (22, 42, 62) configured to support the tool unit; a plurality of bases (23, 41, 61) for contacting with a workpiece, the bases (23, 41, 61) having different shapes from each other; and a mechanism configured to enable the bases (23, 41, 61) to be selectively mounted to a unit support member, wherein: the bases include a first base (23, 61) and a second base; the tool unit can constitute a first configuration of the power tool by combining the tool unit with a unit support member (22, 62) and the first base (23, 61); the tool unit can constitute a second configuration of the power tool by combining the tool unit with an other unit support member and the second base; the other unit support member includes an offset shaft and a transmission mechanism for transmitting rotation of the spindle to the offset shaft; the offset shaft is positioned to be offset from the spindle and is configured to be able to mount a working tool; and the second base includes a relief hole for permitting passage of the offset shaft, the relief hole is configured to be able to hold a part of a grip member when the second base is mounted to a unit support member (22, 62), and the grip member is capable of being grasped by an operator. a tool unit having a rotary spindle; characterised by a plurality of unit support members (22, 42, 62) configured to support the tool unit; a plurality of bases (23, 41, 61) for contacting with a workpiece, the bases (23, 41, 61) having different shapes from each other; and a mechanism configured to enable the bases (23, 41, 61) to be selectively mounted to a unit support member, wherein: the bases include a first base (23, 61) and a second base; the tool unit can constitute a first configuration of the power tool by combining the tool unit with a unit support member (22, 62) and the first base (23, 61); the tool unit can constitute a second configuration of the power tool by combining the tool unit with an other unit support member and the second base; the other unit support member includes an offset shaft and a transmission mechanism for transmitting rotation of the spindle to the offset shaft; the offset shaft is positioned to be offset from the spindle and is configured to be able to mount a working tool; and the second base includes a relief hole for permitting passage of the offset shaft, the relief hole is configured to be able to hold a part of a grip member when the second base is mounted to a unit support member (22, 62), and the grip member is capable of being grasped by an operator. the bases include a first base (23, 61) and a second base; the tool unit can constitute a first configuration of the power tool by combining the tool unit with a unit support member (22, 62) and the first base (23, 61); the tool unit can constitute a second configuration of the power tool by combining the tool unit with an other unit support member and the second base; the other unit support member includes an offset shaft and a transmission mechanism for transmitting rotation of the spindle to the offset shaft; the offset shaft is positioned to be offset from the spindle and is configured to be able to mount a working tool; and the second base includes a relief hole for permitting passage of the offset shaft, the relief hole is configured to be able to hold a part of a grip member when the second base is mounted to a unit support member (22, 62), and the grip member is capable of being grasped by an operator.