A magnetic sensor element using highly-oriented diamond film comprises a magnetic detecting part, at least a pair of main current electrodes for flowing a main current and generating the Hall electromotive force at the magnetic detecting part, and detection electrodes for detecting said Hall electromotive force. Said magnetic detecting part is formed of a highly-oriented diamond film grown by chemical vapor deposition, at least 90% of which consists of either (100) or (111) crystal planes. Between the adjacent crystal planes, the differences {.DELTA..alpha., .DELTA..beta., .DELTA..gamma.} of the Euler angles {.alpha., .beta., .gamma.} which represent the orientation of the crystal planes, satisfy the following relations simultaneously: .vertline..DELTA..alpha..vertline..ltoreq.10.degree., .vertline..DELTA..beta..vertline..ltoreq.10.degree. and .vertline..DELTA..gamma..vertline..ltoreq.10 .degree.. The magnetic sensor element using highly-oriented diamond film has a high heat stability and sufficiently high level of magnetic field sensitivity to be used practically, enabling to expand the surface area and to increase the integration of the element and to measure magnetic field over a wide area and a large space.