伺服電機（servo motor ）是指在伺服系統中控制機械元件運轉的發動機，是一種補助馬達間接變速裝置。
伺(si)服(fu)(fu)電(dian)(dian)(dian)機(ji)(ji)可(ke)使控(kong)制速度，位(wei)置精度非(fei)常準確，可(ke)以(yi)將(jiang)電(dian)(dian)(dian)壓信(xin)號(hao)轉(zhuan)(zhuan)化(hua)為轉(zhuan)(zhuan)矩(ju)和(he)轉(zhuan)(zhuan)速以(yi)驅(qu)動(dong)(dong)控(kong)制對象(xiang)。伺(si)服(fu)(fu)電(dian)(dian)(dian)機(ji)(ji)轉(zhuan)(zhuan)子轉(zhuan)(zhuan)速受輸入信(xin)號(hao)控(kong)制，并(bing)能快速反應，在自(zi)(zi)動(dong)(dong)控(kong)制系(xi)統(tong)中(zhong)，用作(zuo)執(zhi)行元(yuan)件，且(qie)具有機(ji)(ji)電(dian)(dian)(dian)時間常數小、線性(xing)度高、始(shi)動(dong)(dong)電(dian)(dian)(dian)壓等(deng)特性(xing)，可(ke)把所收到的電(dian)(dian)(dian)信(xin)號(hao)轉(zhuan)(zhuan)換成電(dian)(dian)(dian)動(dong)(dong)機(ji)(ji)軸上的角位(wei)移或角速度輸出。分(fen)為直流和(he)交流伺(si)服(fu)(fu)電(dian)(dian)(dian)動(dong)(dong)機(ji)(ji)兩(liang)大類，其主要特點是，當信(xin)號(hao)電(dian)(dian)(dian)壓為零時無自(zi)(zi)轉(zhuan)(zhuan)現象(xiang)，轉(zhuan)(zhuan)速隨著(zhu)轉(zhuan)(zhuan)矩(ju)的增加而勻(yun)速下降。