A pixel-type two-dimensional image detector comprising: a fluorescent material-based heavy particle beam detecting sheet; a lattice-like pixel structure in which a series of reflecting plates that reflect a fluorescent light from the fluorescent material-based heavy particle beam detecting sheet emitting a fluorescent light in response to an incident heavy particle beam are arranged along a vertical axis at a regular interval, and a series of reflecting plates that reflect a fluorescent light are arranged along a horizontal axis at a regular interval and at a right angle with respect to the fluorescent light reflecting plates arranged along the vertical axis, a lattice-like fluorescent light detecting member comprising wavelength shifting fibers formed by providing a groove formed at a front, upper half position or a back, lower half position of the reflecting plates which are arranged in a vertical axis direction, and at a center position in a vertical axis interval for accommodating a single wavelength shifting fiber for vertical axis detection for detecting the fluorescent light, and providing a groove formed at a front, upper half position or a back, lower half position of the reflecting plates which are arranged in a horizontal axis direction, and at a center position in a horizontal axis interval for accommodating a single wavelength shifting fiber for horizontal axis detection for detecting the fluorescent light; vertical and horizontal photodetectors for respective wavelength shifting fibers for vertical axis detection and the wavelength shifting fibers for horizontal axis detection; wherein said fluorescent material-based heavy particle beam detecting sheet for emitting the fluorescent light in response to an incident heavy particle beam is translucent and arranged only at a front surface or at both of a front surface and a back surface of the lattice-like pixel structure of reflecting plates, wherein a fluorescent light with its wavelength converted by and emitted from the wavelength shifting fiber for vertical axis detection and the wavelength shifting fiber for horizontal axis detection may be detected by said respective vertical and horizontal photodetectors to obtain a vertical axis pulse signal and a horizontal axis pulse signal; and an incident position of the heavy particle beam may be determined by applying a coincidence count measurement to the vertical axis pulse signal and the horizontal axis pulse signal. a fluorescent material-based heavy particle beam detecting sheet; a lattice-like pixel structure in which a series of reflecting plates that reflect a fluorescent light from the fluorescent material-based heavy particle beam detecting sheet emitting a fluorescent light in response to an incident heavy particle beam are arranged along a vertical axis at a regular interval, and a series of reflecting plates that reflect a fluorescent light are arranged along a horizontal axis at a regular interval and at a right angle with respect to the fluorescent light reflecting plates arranged along the vertical axis, a lattice-like fluorescent light detecting member comprising wavelength shifting fibers formed by providing a groove formed at a front, upper half position or a back, lower half position of the reflecting plates which are arranged in a vertical axis direction, and at a center position in a vertical axis interval for accommodating a single wavelength shifting fiber for vertical axis detection for detecting the fluorescent light, and providing a groove formed at a front, upper half position or a back, lower half position of the reflecting plates which are arranged in a horizontal axis direction, and at a center position in a horizontal axis interval for accommodating a single wavelength shifting fiber for horizontal axis detection for detecting the fluorescent light; vertical and horizontal photodetectors for respective wavelength shifting fibers for vertical axis detection and the wavelength shifting fibers for horizontal axis detection; wherein said fluorescent material-based heavy particle beam detecting sheet for emitting the fluorescent light in response to an incident heavy particle beam is translucent and arranged only at a front surface or at both of a front surface and a back surface of the lattice-like pixel structure of reflecting plates, wherein a fluorescent light with its wavelength converted by and emitted from the wavelength shifting fiber for vertical axis detection and the wavelength shifting fiber for horizontal axis detection may be detected by said respective vertical and horizontal photodetectors to obtain a vertical axis pulse signal and a horizontal axis pulse signal; and an incident position of the heavy particle beam may be determined by applying a coincidence count measurement to the vertical axis pulse signal and the horizontal axis pulse signal.